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Trans problem or engine problem???

3K views 14 replies 3 participants last post by  rymac 
#1 ·
I've searched this forum numerous times over the years I've owned my truck but never posted. Couldn't find anything similar to my situation so finally had to break down and post. My Tacoma is a 2001 V6, 4wd, 4-door, auto trans with 115K miles. Love it. Bought it with +- 30K in 2005. It has a salvaged title. Recently had the transmission rebuilt after it overheated on me on a long drive from St. George, UT to Salt Lake. Prior to the rebuild it had been shuddering when I was coming to a stop. It was intermittent and at first I thought it was a warped brake rotor or a worn out front tire. After the trans gave out I figured it had to be something with the trans failure. Well, the tranny is "new" and it's still doing it, and it's becoming more frequent. I finally noticed the vibration is caused by the engine almost stalling while coming to a stop as evidenced by the tachometer showing the rpms drop very low. It almost seems like the transmission isn't down shifting. It has never stalled and the engine quickly recovers to a normal rpm. The truck also seems to be in too high of a gear often, resulting in it shifting two or three times when I start accelerating. I've resorted to manually shifting the gear selector to avoid the lugging. I talked to the mechanic who did the trans job and he assures me that it's not the transmission but some type of engine problem that is causing the transmission to select the wrong gear. I don't know that he is wrong, but it sounds like a transmission issue to me. He said he would take a look at the truck to diagnose the problem, but that the repair wouldn't be covered in his warranty because it's not a transmission problem. The guy seems like an honest mechanic and has treated me well so far, but it seems far-fetched that this is not a transmission problem. I just don't know. Maybe I have two separate, unrelated problems? Is there some ecu or other part that could be causing both problems? Could it be as simple as the spark plug wires needing replaced or the MAF sensor? The CEL is not on, and I don't have any diagnosis equipment. Any help would be greatly appreciated, if only just to be more educated when I take the truck back in.
 
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#2 ·
Transmission or engine problem?

I may have posted this in the wrong area originally so I'm re-posting here. I've searched this forum numerous times over the years I've owned my truck but never posted. Couldn't find anything similar to my situation so finally had to break down and post. My Tacoma is a 2001 V6, 4wd, 4-door, auto trans with 115K miles. Love it. Bought it with +- 30K in 2005. It has a salvaged title. Recently had the transmission rebuilt after it overheated on me on a long drive from St. George, UT to Salt Lake. Prior to the rebuild it had been shuddering when I was coming to a stop. It was intermittent and at first I thought it was a warped brake rotor or a worn out front tire. After the trans gave out I figured it had to be something with the trans failure. Well, the tranny is "new" and it's still doing it, and it's becoming more frequent. I finally noticed the vibration is caused by the engine almost stalling while coming to a stop as evidenced by the tachometer showing the rpms drop very low. It almost seems like the transmission isn't down shifting. It has never stalled and the engine quickly recovers to a normal rpm. The truck also seems to be in too high of a gear often, resulting in it shifting two or three times when I start accelerating. I've resorted to manually shifting the gear selector to avoid the lugging. I talked to the mechanic who did the trans job and he assures me that it's not the transmission but some type of engine problem that is causing the transmission to select the wrong gear. I don't know that he is wrong, but it sounds like a transmission issue to me. He said he would take a look at the truck to diagnose the problem, but that the repair wouldn't be covered in his warranty because it's not a transmission problem. The guy seems like an honest mechanic and has treated me well so far, but it seems far-fetched that this is not a transmission problem. I just don't know. Maybe I have two separate, unrelated problems? Is there some ecu or other part that could be causing both problems? Could it be as simple as the spark plug wires needing replaced or the MAF sensor? The CEL is not on, and I don't have any diagnosis equipment. Any help would be greatly appreciated, if only just to be more educated when I take the truck back in.
 
#4 ·
Did the mechanic tell you what he found wrong with it when he rebuilt it?

Had the same symptoms in a 2000 4runner I bought recently. The other owner told me he thought it was tranny. I changed out his shitty Autolite spark plugs and replaced with factory plugs, problem solved.
 
#6 ·
Clean the MAF sensor, and have you ever done the front O2 sensor?

Also, check and make sure the plugs haven't backed out. The 3.4's are notorious for that.

On my truck, it would "stutter" almost felt like the tranny was shifting when it shouldn't. And when I would come to a stop, it would do the same thing, start shaking and acting weird.
 
#8 ·
MAF should be easy to get to. It is right behind your filter box. One black wire that plugs in, and there are two brass screws that hold it into place. Just undo the screws, and pull it straight back. You will see a little filament looking thing in there, that usually gets coated with grime. Get some MAF cleaner spray from walmart, or autozone etc, and spray it down. Just don't touch it or you will kill it.

Front O2 sensor was easy on my 4runner. Two bolts, and one wire plug about 6" away. BUT on my tacoma, the wire looks to be like 2 feet long and disappears up above the tranny, and you cannot reach it. i was told I should go in through the cab to get to the plug after removing the console but I haven't tried it yet. Your truck hopefully has the short wire since it is newer and an AT.

Buy your sensor on Amazon if you do it. Look up your part number on Denso's site, then search for that number on Amazon. It is the "upstream sensor". I paid like $54 for mine, vs $100+ at the dealer.

I would check plugs first though.
 
#9 ·
OK, so I checked all the spark plugs and they were fine. I cleaned the MAF sensor. It didn't look dirty but I cleaned it anyway. I guess the next thing to check is the O2 sensor. If I take the truck into a shop can they test it on the truck?
 
#10 ·
Stupid question, but does your model have the kickdown cable? Maybe that needs to be adjusted? Whatever the issue, it sounds more like problems with the transmission and not the engine performance. Just my :2cents: before you go dropping a bunch of money on parts.
 
#11 ·
yeah, I am just assuming the tranny is good based on the mechanic. I have heard of tranny like symptoms with bad ignition, but sounds like the plugs are good, so...???
 
#12 ·
That's a good question. I have no idea if my tranny has a kickdown cable. I have noticed one more interesting quirk though. If I turn overdrive off I don't get the bogging when coming to a stop. From the beginning I suspected the tranny was just not downshifting to adjust for slower speeds. Almost like driving a manual and coming to a stop in gear without engaging the clutch. That's exactly what it feels like. Like the tranny is fighting the engine and causing it to stall out. For some reason when overdrive is off it doesn't do it.
 
#13 ·
The FSM does indicate you have a kickdown cable. You can check that to be in proper adjustment, but based on the OD issue you just noted, I'm thinking that isn't the problem. You might still have a torque converter issue. The FSM backs up that in the symptom chart.

Torque converters can be designed for different stall RPMs. I'm wondering if when your torque converter was serviced/replaced, if the tech changed the performance of it or replaced it with the wrong converter.

Info on how to check and adjust the various transmission controls-
http://www.ncttora.com/fsm/2003/Repair_Manual/03tacoma/di/ata340ea/preche.pdf
 
#14 ·
I'm starting to wonder about the torque converter myself because the thing shifts harder than it did prior to the rebuild. I don't mind the harder shift because it usually means less wear and tear but it's sounds suspiciously like he put in the wrong one. Maybe from a different year or from the two wheel drive tranny.
 
#15 ·
Ok. So I took my truck in to the shop that did my transmission and they told me that the transmission is operating perfectly, but the engine is running lean and missing, and that's causing the shifting problems. They said the MAF sensor is all over the place, which must mean I need to replace it because I already tried cleaning it. They also said the throttle plate needs to be cleaned, which I have no idea how to do. He also said to replace the fuel filter because he suspects that my fuel pressure is low. He said he didn't test the fuel pressure, but due to the way the truck is running he thinks there's a pressure problem. I told him that from what I've read about the truck it's supposed to have a lifetime fuel filter, which he claims is impossible. He said the fuel pump itself could also be a problem but he didn't test it. He said the 02 sensors are lean due to the engine running so lean, but don't need to be replaced. I think I'll start by cleaning the throttle plate since I'm assuming all I need for that job is throttle body cleaner. I'll check into a new MAF and fuel filter as well and hope that solves the problem. How do I know if this fixes the problem of the engine running lean? I assume I'll have to take it to a shop and have them hook it up to a computer to test it? Is there a better way to do your own work or will I always be at the mercy of a shop with a computer? I'm going to start searching the forum now for help on all this stuff but wanted to give an update to those that have helped so far.
 
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