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Discussion Starter · #1 · (Edited)
For those of you that have never heard of this issue please read the following:

http://www.tacomaterritory.com/forum/showthread.php?t=13283

Note this only affect 2003 and 2004 tacomas with the throttle by wire system on a 3.4 engine.

Assumption:
I have only heard of supercharged engines that are having problems with this type of throttle set up. There are various configurations ranging from electric fans to TRDs 7th injectors, but the one common thing appears to be a supercharger.

If you read the thread above you will be able to see the differences between the TBW and mechanical set up, but the ones I will highlight will be the butterfly motor that is controlled by the ECU, the APPS that is read by the ECU, and the addition of coolant lines on the TB housing. The assumption I am making is that this butterfly motor need to be at a certain temperature to operate correctly(actual temp unknown – if someone has the means to find out this information please chime in). I’m assuming the coolant lines were added to bring this motor up to operating temperature in those extremely cold conditions.

Problem:
With all the information gathered from the link above, the problem appeared to be the rheostat/potentiometer within the APPS. I asked the question about the difference in temperatures between a supercharged and non-SCed engine(no answer), so I became curious. Since this APPS is made of plastic I figured extremely hot temperatures would not be a good thing for it and MAY be the cause of the problems everyone is experiencing. For those that are already experiencing this, sorry, but I don’t have any additional information on the fix other than what Dennis Dawg has already mentioned in the link above. However I do have a theory on the cause with some test results to back it up. Once again this is only a theory and I have only performed one test from a series of test I plan on doing.

Theory:
Just think for a moment, aluminum is a good heat dissipater. If you look around most heat sinks are made of aluminum. The stock intake plenum is one big block of aluminum, or heat dissipater. It would not only dissipate the heat of the engine but the heat of the TB(brought about by the 180 degree coolant flowing through it). Because of this, the TB itself would probably never reach 180 degrees(all temps mentioned will be in Fahrenheit) and the designers must have kept that in mind when they decided to bring the motor up to operating temps with coolant that high. This is why I think NA engines are not reporting problems. Now let us take a SCed engine. With the addition of a supercharger you are introducing a heater. The SCer is just one big compressor. When you touch the motor of any compressor you will see it gets really hot. Aside from the additional moving parts(frictional heat) you are introducing heat cause by this boost in pressure(higher the boost the higher the temperature). By bringing up the temperature of the supercharger you are bringing up the temperature of the throttle body mounting plate. This now goes from a heat dissipater to a heat generator. Now the TB sees 2 heating devices. Lets keep in mind the TB itself has very little moving parts so negligible frictional heat. Also the TB is made out of aluminum so it will be dissipating heat as well.

Test #1 results:
I have a supercharged 3.4 with URD fuel upgrade kit and 2.2” pulley. No water injection as of yet. Talk about a heater. Now just to be fair, I will mention that I do have a Teflon gasket that someone on this board was selling last year to keep the supercharger from getting the heat from the engine. I can’t say for sure if this is helping, but I figured I would mention it. Now back to the test. I purchased a 4 channel thermocouple thermometer from Omega to monitor several different points. First thing I did was monitor the inlet and outlet temps of the TB coolant lines. As per my theory, the outlet was about 2-3 degrees cooler than the inlet, thus noting heat transfer from coolant to TB. For the record the test was performed at night with ambient temperature at about 60-70 degrees. The coolant temps hovered at around 169-174 degrees(I have a 170 degree thermostat). I placed another temp sensor on the top of the TB right next to the APPS and another one on the top of the supercharger itself. Another thing to add here is that the thermocouples where attached using duct tape(This was suppose to be just a quick test so I figured duct tape would work ok – I will mention when I think I had a problem). The top of the TBs temp was about 120 degrees at highway speed while the supercharger was about 130-140 without going into boost. At about 4-5 seconds of full boost(9psi) it went up past 155 degrees. The TB followed up to about 137 degrees. While going up hills and maintaining a boost level of about 2-3 pounds the supercharger was operating at 155 degrees. The top of the TB appeared to track the SC in that it would increase about the same amount. Another observation I made was at idle the top of the TB would go up slightly which was not surprising, but when I would turn off the engine the temp would shoot up to about 160 degrees at the TB(This is hotter than the SCer). Theory there is that the air from the fan(or highway speeds) would cool off the surface of the TB(where the thermocouple was). I have the stock fan, but will soon be going to an electric fan, I suspect that an electric fan can possibly make the TB run hotter during the slower speeds. Yes the electric fans turn on at slow speeds, but it doesn’t have a constant air flow like a mechanical fan does. Ok, moving on. I figured the temps of the coolant were of no more use to me since they appear to be pretty consistant and always appeared to be 2-3 degrees cooler at the outlet(always heating). The SC was always a few degrees hotter than the TB as well(always heating). I was curious how the bottom of the TB was doing(near the inlet/outlet but still close to the APPS). I put a probe on the TB at the bottom about the same distance from the APPS as the top thermocouple. I wasn’t able to test uphill temps at boost since I was on my way back down at the time(going home from Big Bear), but the bottom was always about 20 degrees hotter and reached temps of up to 150-something. This is where the problem with duct tape comes in, after about 157- degrees, and 30 minutes of driving, the temps at the bottom were no longer 20 degrees hotter than the top. They were about 10 degrees hotter now, but I figured it was because I was driving downhill and it was actually running cooler now. When I got home I realized the duct tape came off an the TC was just hanging there(getting the temp of the air under the TB). The air under the TB was still hotter than the top of the TB(I assume this is the hot air from the engine block). That is why I think the air flow from either the fan or just highway driving helps the top of the TB, not the bottom.

From all this information I gather the TB is seeing hotter temperatures than expected by the designers when paired up with a SC. I will be installing an electric fan and removing the coolant lines to see the effects on the TB. I would expect at warmer climates the coolant lines can be removed with no ill effect (but most importantly a positive effect). I will try to see if I can find someone with a NA engine to do a baseline test. As of now I want to hear your comments and possibly some ideas of what else to look for as possible cause, or just what other tests to perform. I don’t have much time outside of work and I don’t drive my truck to and from work because of these damn gas prices, but I will try to do as many test as I can. For those of you who don’t want to reply here on test recommendations or comments please PM or e-mail me through my sig.

For those of you that have the 05’s I hear you have a TBW system as well, but not with a cable like ours. The APPS(or system that replaced it) appears to be elsewhere, so I don’t think you guys would have this issue even if a supercharger ever comes out.
 

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I've read of several bone stock trucks having this problem, not just S/C
 

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Discussion Starter · #3 · (Edited)
If so, please let me know were. The more information we have the sooner we can find out the cause to this problem. As I mentioned before I plan on doing some tests on the NA engine as soon as I get a hold of one. For now, all I can go with is what I have read or done myself, so please give me the link or tell them to chime in.
 

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I get emails all the time from people with this problem that do not have a supercharger.

The problem is a faulty design. It is just that simple. You will notice that they dumped that design already.
 

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Discussion Starter · #5 · (Edited)
Ok I will buy that, but for those of us that are stuck with it, I am trying to find out where the design flaw is. It appears as though Toyota isn’t doing anything right now to remedy or fix it. They don’t even appear to know anything about it. Faulty ECU that will kill your engine all together is something simple to prove, but an intermittent problem like the one most people are experiencing is another story. Call it curiosity or preventative measures in my part, but I am trying to find the actual cause before it becomes an issue for me. I cannot just take it as a faulty design and say, "Oh well, thats just the way it is." Another thing I might add is I am not experiencing this problem as of yet. I only have 20K miles on my truck and I’m trying to catch the problem before it becomes one. So if anyone has useful information like the one Dennis has posted please let me know so I can run other tests.
 

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I will bet you a box of donuts that they a fully aware of this. I will also bet that "they" read this as well as lots of other forums all day long.

I am also sure that they have held high level meetings about this and do in fact have a plan of action for it. You are seeing this plan of action in full force.
 

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Discussion Starter · #7 · (Edited)
Ok you're on. A box of donuts it is,... only if we agree on Krispy Kreme :) I am still not convinced it is not thermo related,... even if stock trucks are reporting this.

From what Dennis reported on the other thread, what we have is a closed loop system consisting of a rheostat(sensor), and ECU(controller), and a motor(item being controlled). In my quest to research this issue, the set up he mentioned was verified several times(one example):

http://www.sae.org/automag/techbriefs/02-2002/

My favorite line is:

"After a number of years of offering this, we've got the data on what the failure rate is," said Williamsen. "It is pretty low."

I also read this:

In the event of an error in the signal from one of the position sensors, the ECM can switch off the throttle-control servomotor and modulate power through the fuel-injection and ignition systems.

It sounds exactly like what people are experiencing. Now if the sensor(s) is/are a simple pair of rheostats, then I can only see 2 possible problems: a bad spots(broken trace of some sort) or misalignment issue like Dennis mentioned and going out of the specified impedance values(confusing the ECU). Either of these two cases can be caused by thermal-cycling or extreme thermal conditions.

I will also add that the new system appears to have the APPS in the actual pedal now(away from heat sources or extreme thermo cycling). Until someone can convince me otherwise I will continue with temperature testing.
 

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It does not matter if it is heat related, vibration related, or what ever related. In the end they crap out and need to be replaced. In the end they do not serve the intended use reliably and Toyota does not make them any more. That should be a clue.
 

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Discussion Starter · #9 ·
I’m sorry, but I will have to disagree with you on this one. Intermittent problems that have come up are hard to prove and the service department will not replace something on your word alone. During the time they are intermittent they are a safety hazard. I am sure if you would ask Nags, Dennis Dawg, Wisctaco04, LocoTaco, Super Doody, and anyone else that is having this problem if they would like to have postponed this problem with something as simple as removing the coolant lines, would they have done it, what do you think they would say? (keep in mind I am not making this claim, but I am trying to figure out the problem to see if something that simple will help) I have 20K miles on my truck right now and if people are having problems just a little after the 36K mile warranty goes out then I am almost due. I am not trying to fix this issue for Toyota by any means, but if I can get another 10K miles of safe driving out of my TB by a simple mod, you bet I will do it. By then hopefully Toyota would have lived up to its reputation and fixed the unreliable issue of their design. So yes the cause does matter should I be able to gain additional safe miles out of a simple mod.
However, it appears as though there is really no interest in this, so I will not report any more results should I decide to continue my quest. Good luck to everyone with this problem and to those that will have this problem in the future.
 

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No reason not to think about it and troubleshoot some. It can be fun!

I believe that heat could be a factor. Though I believe it did this off and on for months, the two times I noticed the problem was most severe was when I was driving at rather fast highways speeds through the desert, once south of Baker, Ca and once in Arizona the way to Sedona. These were both very hot days.

The APPS has very little holding it together. It is all-plastic with no noticeable screws. so the rheostat can spin in its plastic housing, or at least it did on mine. It could be that the adhesive they use in the part heats up and gives way.

However, the temperatures you measured do not seem high enough to cause a problem, in my opinion. but, at the same time, using a thermocouple in this situation can be a difficult because of the moving air that may cool it, it not being immersed in the matter being measured . . . many factors could make the temps seem lower than they are. I have run into similar issues at work.

The APPS when mounted is partially housed inside the TB. It could be in that little pocket the trapped air and the surrounding matter is much higher than other areas of the TB, S/C and engine. There is no air flow inside there. The metal ARM of the APPS may transfer heat energy to the interior of the APPS and cause the failure. A guess.
 

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DennisDawg said:
I believe that heat could be a factor. Though I believe it did this off and on for months, the two times I noticed the problem was most severe was when I was driving at rather fast highways speeds through the desert, once south of Baker, Ca and once in Arizona the way to Sedona. These were both very hot days.

I don't know... I just don't buy the heat thing.. The very first time my truck ever did this was on an Early Febuary night a few years back in Central Florida. Temp at the time was about 40f and I was cruising on the highway at bout 80mph.
 

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DCabTaco said:
However, it appears as though there is really no interest in this, so I will not report any more results should I decide to continue my quest. Good luck to everyone with this problem and to those that will have this problem in the future.
Easy there Dcab!! We appreciate your testing this theory out. You and I have discussed this and you know my feeling on the issue. I for one would like to find a cause and cure because it looks like Toyota hasn't come up with anything better than swapping out bad throttle bodies with ones that are destined to go bad. I think high heat over an extended period of time has something to do with this. I for one am very interested in your findings and if you decide not to post them, please keep me advised via PM, E-mail, or phone.

Dave
 

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Discussion Starter · #13 ·
Hey Dave, I was just messing with Gadget. I remember a guy a few years ago that was investigating a lean mixture and pinging on a supercharger design(well to clarify it was a bad package design since it was incomplete) where the vendors themselves would deemed him crazy. Yet for some reason that supplier ended up using some of his findings then went off and developed their own fix. While still not a good fix(at least not the controller) it was their answer to the “problem” they said he was crazy for bringing up. Had he just sat around and waited for them to develop a fix, he might have gone through a few heads by now at the very least. We are dealing with more of a safety issue and a totally different company, but I still don’t plan on sitting and waiting around and possibly paying out 650-1000 bucks for a TB when it goes out. So Gadget, once Toyota comes out with the fix I will personally take your box of krispy kreme donuts down to your Southern California office when you make your way down here. Deal? :)

As per my next steps, I plan on installing the electric fan to see if it has any effect on the TB. I suspect it will affect at least the surface temps at slower speeds(I don’t think this is too much of a big deal though). Once that is verified I will see how much of an effect removing the coolant lines will do. I have various ideas on possibly stabilizing the temperatures and keeping them down. We’ll have to wait and see what comes about from these next few tests.
 

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Discussion Starter · #14 ·
Dennis, I agree that the temps I posted don’t appear to suggest any issues, however lets take extremes now. Imagine for a moment a truck with a SCer, 2.0 pulley, electric fan, no water injection, and a 180 thermostat with coolant lines plugged in. Now lets say it is a hot day around 100 degrees. After a good 30 minute long drive in the highway and everything is up to operating temperatures the person stops the truck to pick up a soda at the corner mart. Truck is off for about 5 minutes and the TB is up at around 180 degrees(like my test suggested the TB goes up in temp when engine just turns off). Now he continues on his trip through the mountains where he has to put it into boost and a few WOT situations to pass the slow big rigs. I suspect the TB is now well over 200 degrees. Now all that I have described is real life situation that I myself have gone through. In fact it happened just a few weeks ago when I went up north to the bay area. Granted I don’t have an electric fan and I have the 2.2 instead of the 2.0, but you can understand what I am getting at. Oh and I agree with you that the TB surface temp will be cooler than the actual TB itself. The test I performed were something I put together in a mater of 10 minutes since I had just gotten the thermometer and was on my way to the mountains. I posted all this info up to see if anyone had any suggestions as to where and how is the best place to mount the TCs.
 

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To counterbalance your data, mine never had an episode occur after parking the truck and restarting. It all ways occurred when rolling, usual for some time. It would seem as if my foot had slipped of the accelerator and though I had that feeling many times, it was only a complete failure for which I pulled over two times as previously presented.

As others have posted that is was cold when it occurred to them, that might rule out temperature as the lone mode of failure. We’d need to track the reports to get a handle on that.

Another possible issue may be vibration and possibly dirt. Rheostats do get bad spots in them from being in the same spot all the time and even more so if dirt is present. I know that removing the APPS on my truck revealed dirt in the TB where the APPS engages the throttle. That may cause some of the problems.

In that case, with the APPS in a bad spot, the computer could shut down the throttle motor. The same would be true if the rheostat was dirty, it might cause an open and subsequent motion caused by a change in accelerator position might move of clear the dirt. Turing off the truck and restarting would then find the APPS is a better spot or not engaged in dirt, and the system would return to normal operation.

However, I still believe my APPS had rotated in the housing. Could it be that when it hit a bad spot, the computer shut the throttle motor down and I then pushed harder an the accelerator, making the metal arm of the APPS engage the throttle but also putting enough considerable pressure on the rheostats mount in the plastic assembly to turn it? If it experience that same throttle issue again, then I’d expect this to be the case, but the cause of the shutting down of the throttle motor would still be unknown.
 

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Discussion Starter · #16 ·
Nags,
Ok well I will try to describe different scenarios that may help you understand my ideology. It will not only help you see why I think it is temperature related, but it will help reassure me of my theory.

Where I work we deal with latent failure all the time. Most of which are caused way before the problem is ever noticed. Let us take ESD sensitive devices for instance. If not properly handled and the proper ESD precaution are not followed you can potentially inflict a hairline fracture, or any other latent failure, on the device that while it will not completely make it inoperabl, it will make it unreliable.

Here is a real world example for you that will show you just how temps can affect different things. I consider Sony to be a very respectable company when it comes to electronics. I purchased an early 90’s Sony Trinitron during my high school years and planned on taking that TV to my Dorm at college. Well just about 1.5 years after I bought it(it only came with a 1 year parts and labor warranty) the picture went out. I would get just white noise, fuzz, snow, whatever you want to call it. However the RCA input still worked and after having the TV on for about 10 minutes the picture would work again through the regular RF tuner. It turns out that they had either a design issue or a manufacturing issue where the thermal expansion/contraction of the materials in and around the tuner would cause the solder joints to develop cracks. Slowly these crack would get bigger and deeper until the solder connections would no longer make contact. So the picture wouldn’t show. Now after it was on for a few minutes everything in there would warm up and the solder(metal) would expand just enough to make a good contact and the picture was back and crystal clear. Now you tell me when was the problem inflicted? Was it upon initial turn on when the picture would not show? No, it was through this thermal cycling that eventually led to a crack on the solder joint and then the effect was experienced when it was cold. So the effect you are experiencing when cold may have been caused by something previous to that situation. Now just to let you know what happened with the TV situation, I just took out the tuner re-flowed the solder and all was good again. Should I have taken it in I would have paid 50-100 bucks for the diagnosis and about 90 and 100 bucks for each module. The tech would not have re-flowed the solder. They would diagnose it down to a line replaceable module and just buy a working one. Being a college student I had no money to take it to an electronics shop. Guess how I found the problem and fix for this TV? That’s right on the internet. Just look it up. Do a search for Trinitron solder problem or something like that. So you tell me, could we be dealing with a thermal cycling, extreme temps, or even prolonged high temps like Dave mentioned? I think it is a possibility still so I will continue with my investigation.
 

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Discussion Starter · #17 · (Edited)
DennisDawg said:
To counterbalance your data, mine never had an episode occur after parking the truck and restarting.
I agree with you on everything and just to clarify, I haven't experienced the symptoms you and everyone else described. The point I was trying to make when I said I turned off the engine for 5 minutes is that my test data reported the temp of the TB shoots up right after you turn off the engine. Then upon turning it on the SC is in boost rather quickly and then at full boost a few time during a trip. This could make the TB go to extreme temps that I haven't tested yet. I was stating a "for instance" where the TB would see extreme temps and possibly cause a latent failure. You wouldn’t necessarily experience the symptoms right away, but it could “for instance” make the epoxy of the rheostat hot enough to lose its holding ability, then lose its spot like you mentioned… I don’t know. I am still just brain storming and throwing out possible causes. The one thing I do know is that WHEN you experience the symptoms doesn’t always mean that is the exact time the problem was inflicted.

You do bring up a very good point about the dirt issue. That would definitely cause the symptoms you are experiencing.

If you suspect a bad spot on the rheostat, then maybe that could be a test you can perform.(since I am not experiencing that problem anymore) You would have to attempt to either sweep the rheostat or monitor the output with a device like a data logger. If you start experiencing the problem again let me know and we can come up with something.

From all the possibilities that are coming about I think the new design that is in the 05s is not susceptible to any of that. When you take the APPS out of the engine compartment and most importantly out of the engine, you don’t have the heat, vibrations, and dirt it would have otherwise been subjected to. It wouldn’t surprise me if Toyota would just relocate the APPS as their fix.

Another question for you Dennis would be, does our APPS have 2 rheostats like mentioned in the article? From the FSM I would guess it only has 1 rheostat. I haven’t taken mine apart, nor have I checked the values yet, so I wouldn’t know.
 

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Discussion Starter · #18 ·
Something else I forgot to mention is depending on what material this rheostat is mounted on, it could possibly cause bowing(once again when things cool off or return to normal operating temps, so latent in that respect). Which in turn can cause the incomplete contact throughout the entire sweep. I can see many many possibilities that can occur and be temp related. That is exactly why I decided to start with temp testing.
 

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DCabTaco said:
However, it appears as though there is really no interest in this, so I will not report any more results should I decide to continue my quest. Good luck to everyone with this problem and to those that will have this problem in the future.
Whao, wait for me. As it turns out I just got back in town from a little road trip up north. Temps on the way up were in the 60's with a helluva tailwind. I stopped for gas once. Pulling back out, the throttle did the crap out on me again! I was kinda freaking out since my plan was to head to the Natl. Forest and hit some back-country trails. Not a good place to be with 1/4 throttle. I chickened out and stuck closer to the main branches. It crapped out on me one last time before leaving the nearest town heading into the woods. For the rest of the trip no other crap-outs but it stayed cooler but less wind. On the way home I had no problems either. It was windy as all hell on the way home but i never stopped so I have no idea if it would heat up sitting still for a short pit stop. My old Jeep used to overheat sitting still "off" so I can assume some of the same effects a still fan will do on our engines. I still have my coolant lines hooked up since I live in the icebox zone.

I have one of the teflon gaskets as well I will put on soon. I just also ordered a peice of G-12 poly-phenolic to replace the aluminum TB spacer the WI runs into. Maybe the insulating properties of the plastic will work better than that of aluminum. I will give an update after I get it machined out. The next step may be glass scooped hood if the above 2 mods don't cool it enough.

Matt
 

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Discussion Starter · #20 ·
Matt, The thermal issue I suspect may be more of a cause, and irreversible damage. In other words simply by just keeping it cool from now on may not fix the problem as it has already done it’s damage. Since it appears as though you are experiencing this do you have access to a data logger of some sort? Kind of like the LM3 that innovate makes. We can tap into the output of the APPS and see if there are any inconsistencies. The output should always be a smooth line following your pedal. The output voltage should stay within 0 – 5V. I have found another site with more information on the APPS and it appears as though the APPS may be exactly like the TPS. Nonetheless, you can help us determine if the APPS has bad spots. If you’d like to discuss this further PM me and I will tell you what I think we can do to monitor this.
 
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