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Discussion Starter #1
I'm putting this out there hoping someone has more easily solved a similar problem. Please pardon the length; the details may be important.

I bought my truck about a month ago and patiently waited until after it passed the smog test to do anything to it. It ran fine - just a little rough. It has 90k on it and looks like it has lived on a ranch for most of its life (dead rear shocks & springs/dead mice in the air intake/tumbleweeds stuck up in the frame). Since I got it for much less than resale value due to the impending maintenance needs and some other performance/body issues I don't really care about throwing wearable parts at it because it needs them. With that being said, heres the deal:

The first thing I did was to check out the airbox which had duct tape around the MAF housing and the airbox itself. Turns out the whole thing was cracked off and held on with several layers of various tapes and screws. A liberal dose of JB-Weld cured that. While that cured overnight I had the MAF Sensor out and decided to clean it. Got some of that QD electronics cleaner and cleaned it up per the instructions on 4x4wire. Just a note, that airbox crack must have been there a loooong time cause there was dirt coating EVERYTHING.

At this point I realized I had my work cut out for me and decided to see what performance changes could be realized from each individual part swap. So I pulled the EFI RELAY not the fuse (I know better now) and let the truck sit overnight while the JB cured.

I popped everything back together the next day and started her up - MUCH SMOOTHER. I couldn't believe the difference! BUT, the second I touched the skinny pedal the engine revved up to 2000 rpm and stayed there, permanently.

Now, like I said, the truck has 90k on it and I remember reading something about the ECM having to relearn all the trims etc. I didn't think much of it and thought it would slowly go away. In the meantime I:

Cleaned the TB
Replaced the TPS (It did have a dead spot)
Changed the oil, oil filter, plugs, wires, air filter, fuel filter
Flushed the radiator and put in a new thermostat
Replaced rear suspension
Bled brakes
Checked for vac leaks
Checked all the sensors I could reach with my DMM for proper tolerances

Now the engine runs even smoother but the idle never went down. Before I threw any more parts at it I decided the pros needed a look so I took it to my mechanic. The verdict: no vacuum leaks, no codes. He thought it might be the TB because when you tap on it the idle drops to 1250 but any gas and its back up to 2k.

DesertTRD helped me out since he had a similar problem and after a new IAC Valve the problem is down to 1500rpm.

From searching I also learned that the O2 sensor needs to be replaced after about 75k miles so I did that (What a difference too!)

Last night I left the EFI fuse out; popped it back in this morning and I get a new behavior. Still 1500 rpm idle but now when I come to a light and press in the clutch the idle goes down like it should but when it hits ~1000 rpm it jumps to ~1250 back down to ~1000 then up to 1500. :mad: I've been following this thread which seems to have similarities but no suggested remedies as of yet.

The thing of it is - it feels like a vacuum leak. Smooth (albeit high) idling until throttle is applied then the performance feels choppy, especially in third gear). I've checked for leaks half a dozen times both visually, by feel, and by disconnecting the IAC and running a torch over all the hoses.

The only reason I am hesitant to replace the TB is because I took the damn thing out and cleaned it, polished it, greased it and everything was operating normally. The only possible anomaly I could find was that the butterfly valve was not completely airtight, I'm not sure if this is normal but the plate in there didn't look worn and neither did the chamber on the throttle body. Also, all I did was clean the MAF to start the problem, I'm not sure this has anything to do with the TB.

Here are my next steps:
1) Check for vac leaks ONE MORE TIME (FREE)
2) Buy this scan tool so I can see what the ECM is seeing ($90)
3) Assuming there is nothing wrong from the scan - take my mechanics recommendation and buy a new TB ($600 unless I can find one at the yard)
4) Take it to a dealer

I'm hoping someone has some addition info to keep me from having to spend any more money so I can get started on my front suspension, tires, sliders, and skid plates and actually do some wheeling this spring!!

:boobies: :driving:

Again, sorry for the long post but details may be important :confused:
 

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Discussion Starter #4
AK98Taco said:
Yeah, those were the first things I did. The IAC checked out but I ended up replacing it anyway. The throttle body checks out too (at least the things the FSM instructs). Also, I don't want to mess with the idle adjust screw because it was running fine before I cleaned the MAF Sensor. I thought maybe there was such a huge performance gain from cleaning the MAF I needed to back off the idle screw a bit but when I looked it still had untouched factory sealer on the threads.

4xClover said:
Maybe you have excess cat fur in the engine?! :D
:p Quite the opposite in fact, my cat was the one that found a mouse nest under the airbox (they were already dead but it wasn't fun cleaning out). Oh, and I did check for chewed wiring and shorts.

Thanks for the ideas though.

From what I've read, each high idle problem has its own unique quirks, I'm hoping someone has seen these symptoms before. :dunno:
 

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i recently did the same thing the other night while cleaning my maf and throttle body and run into the same problem. i dug around and fount a little vacume line that i had accidently pulled off up next the the intake tube where it goes into the throttle body and conects to a piece almost up under it, hooked it back up and the idling returned to normal. this might be what the other guy was talking about. i am no mechanic but it did solve my problem and hope it helps with yours...let me know.
 

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Discussion Starter #6
cmize said:
i recently did the same thing the other night while cleaning my maf and throttle body and run into the same problem. i dug around and fount a little vacume line that i had accidently pulled off up next the the intake tube where it goes into the throttle body and conects to a piece almost up under it, hooked it back up and the idling returned to normal. this might be what the other guy was talking about. i am no mechanic but it did solve my problem and hope it helps with yours...let me know.
Thank you cmize!! That is actually a HUGE help! If I could isolate the hose that causes the problem I can more easily find what I suppose to be a vac. leak. I got home a little late tonight so I will have to wait till after work tomorrow to do some testing :) Are you talking about the tiny hose (about 1/4") that comes in off the top of the TB and connects to the actuator just to the left of the intake to the TB or the larger air assist hose that comes out of the very bottom of the TB?
 

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On my 98, I had a high idle problem right after i put my S/C on. I found out the that vacuum line going to the diaphram that closes the throttle plate the whole way was plugged. I put a new line on and the idle dropped to normal. It's a little vacuum diaphram on the bottom backside of the throttle body. Check for vacuum at that hose. i would bet that is your problem. Either the hose of the diaphram itself. Another easy thing to do is to try to manually close the throttle by hand. The vacuum actuator is supposed to pull it the rest of the way shut but without a strong vacuum signal, it will not do so. Good Luck.
 

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thermostat stuck slightly open......caused mine to idle high..............but chck

throttle cables , body etc.

follow ak98's advice then go from there.
 

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Discussion Starter #9
Special thanks and props to cmize and tacokid!! :clap: Thanks to everyone else too! I got home, checked that tube for leaks, put a vacuum pump up to it, and ran that actuator through its paces. Put the tubing back on and the engine started up right at ~800rpm.

I thought to myself no f$%^ing way was it that easy!! I drove around the block and the problems started up again so I left the engine running and put my gauge on that tube - ~17".

I don't know if this is weak because it isn't discussed in the FSM (that I know of) so I pumped the actuator again a few times, put the tube back on, voila.

I'm not sure what is causing the sticking so I am going to take my TB off to see what I can see and hopefully clean that out. It would suck to have to buy a whole new throttle body for that one little part.

You guys just make a very stressful month a million times better :D :D :D :D
 

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Discussion Starter #10
OK, so I've got some serious newbie embarrassment going on and wanted to fess up to help (hopefully) any other newbies from making the same mistake.

First lesson: Do every step of the FSM exactly how, and in what order, it says it.

I had done every step of the Throttle Body inspection - except Step No. 2 - "apply vaccuum here" since my vac. was all the way downstairs in my shop :eek: Even though I checked for operation on the bench later if I would have done this on the engine while the truck was running I would have solved this right away.
Second lesson: If you trust your mechanic with your life why can't you trust him when he says, "You need a new throttle body"?

I figured the problem was something related to cleaning the MAF since that is when the problems started - I hadn't even touched the throttle body yet. Well, it turns out that my TB is all gunked up and the vacuum is having a hard time closing it that last millimeter.
I took everything off last night and greased it up but it just isn't enough. I'm hesitant to disassemble the actual throttle body with all the springs in tension and all.

Has anybody taken theirs apart and successfully put it back together? I'd really like to try and clean it - I'm going to check the yards for a used one but if that doesn't work I'm stuck with a $600 bill for a new one and there goes the $$ for my front suspension for the next couple months.

Thanks again everyone - even if it isn't fixed yet it really does feel good to know it is solved. Oh, and I also know a hell of a lot more about my engine! :rolleyes:
 

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Denver Dave said:
OK, so I've got some serious newbie embarrassment going on and wanted to fess up to help (hopefully) any other newbies from making the same mistake.

First lesson: Do every step of the FSM exactly how, and in what order, it says it.

I had done every step of the Throttle Body inspection - except Step No. 2 - "apply vaccuum here" since my vac. was all the way downstairs in my shop :eek: Even though I checked for operation on the bench later if I would have done this on the engine while the truck was running I would have solved this right away.
Second lesson: If you trust your mechanic with your life why can't you trust him when he says, "You need a new throttle body"?

I figured the problem was something related to cleaning the MAF since that is when the problems started - I hadn't even touched the throttle body yet. Well, it turns out that my TB is all gunked up and the vacuum is having a hard time closing it that last millimeter.
I took everything off last night and greased it up but it just isn't enough. I'm hesitant to disassemble the actual throttle body with all the springs in tension and all.

Has anybody taken theirs apart and successfully put it back together? I'd really like to try and clean it - I'm going to check the yards for a used one but if that doesn't work I'm stuck with a $600 bill for a new one and there goes the $$ for my front suspension for the next couple months.

Thanks again everyone - even if it isn't fixed yet it really does feel good to know it is solved. Oh, and I also know a hell of a lot more about my engine! :rolleyes:

I believe Showstop can give you a good step-by-step on the TB work ;)

My guess is that butterfly not closing quite right or you need to give the outer linkage a good squirting with carb cleaner while working it back and forth.
 

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Discussion Starter #12
Update:

Well, I haven't found the right model of used throttle body yet and I refuse to pay full price for a new one so I guess I'm waiting this out. In the meantime I took a spring that was in the crap drawer and found some stock places to attach it. Problem is solved for now but the gas pedal is a pain in the ass to use. Tomorrow I'm going to adjust the tension of the spring to see what I can get away with.

The $600 spring:
 

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Any update to your problem? I'm having similar high idle problems and would like to know what your resolution was.
thanks
 

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I had the same problem. After cleaning the throttle body, it took a couple days for some of the crap to break down. It's been running ok for a couple days....just keeping my fingers crossed that it's gonna be ok now.
 

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Discussion Starter #15
Any update to your problem? I'm having similar high idle problems and would like to know what your resolution was.
thanks
The spring is still on there. I've been keeping an eye out for used throttle bodies on here, e-bay, and CL. Bought a few of them but they ended up being slightly different; different enough they didn't quite fit. I'll probably flood the For Sale section here in short order with used throttle bodies :eek:

My PS pump started to go around the same time this happened and, in researching the PS system, I read that the ecu will compensate idle speed to get enough pressure in the rack. I just replaced the pump not too long ago and was planning on taking off the spring to see if that was my problem. I doubt it will work but I'm giving it a try this weekend anyway. I'll post the outcome either way.

I hope you get your problem resolved (pita isn't it). If you do please let us know :)
 
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