Puzzling Problem

[Lexor]

My '93 SC300 (175,000 miles, original owner and have had the car maintained by Lexus all its life.) has a jerking problem that is occuring upon lightly applying pressure to the throttle when driving, no matter what speed. If I apply moderate to hard pressure to the throttle, no problem. This jerking does not occur on ever start. Only about 1 out of 6 starts does it do this and it will run that way continuously through the same start. All other times, no problem. I have recently found that when the problem occurs I can stop the car, turn off the engine, restart the car, drive away and the problem is gone.

I have taken the car to 2 different Lexus Dealers to repair this problem. Each said that I had a Head Gasket issue that needed repaired. After spending $5,000 in replacing the Head Gasket and other service repairs, I still have the original problem (however, the car is running great now when it is not jerking). The Lexus Dealer that I had repair the Head Gasket can not figure out the problem, because it can not be replicated every time.

This is puzzling because of the inconsistancy. Has anyone else run into this same issue?

Also, today at lunch it starting jerking again. Instead of stopping and turning off the engine, I put it into neutral, then back into drive and the jerking on light throttle pressure stopped. I was not able to replicated it after that. I plan to continue this avenue of testing in order to narrow it down.

Lexor

[AWJ]

Sounds like the fuel pump ecu thing again. The dealer you took it too did a lot of unnecesary work. I'll see if I can dig up the threads we discussed it on. Otherwise try a search for fuel pump relay or something like that.

[AWJ]

Here is the fuel pump info.

Fuel pump info

It could be your torque converter, transmission, or differential also. Did the dealer even test anything or did they just go and replace the headgasket? Since it is intermittent, it could be a solenoid valve in the tranny.

[Lexor]

Thanks AWJ for your reply.

My thinking is that it is not the fuel pump ecu. The reason is that when I run the engine in neutral or park, the engine runs smooth... no hesitation or jerking.

I initially thought that it might be the torque converter, but when I read up on torque converters and how they work... it seemed that if it was failing there, then it would happen continously.

I think the next place for me to look at is the solenoid valve in the tranny. Are there tests that can be run on this?

To answer your questions about the dealer... yes, they ran tests.. mainly on the engine though. Not sure they ran any tests on the tranny. The main problem at the dealer was that they were not able to replicate the problem each time I took it there.

[jimbostar]

How about an oxygen sensor? This might be the first symptoms.

[AWJ]

Oxygen sensor should throw a code. Did you do an mil check? Try that first. I have the procedure if you need it. Also, you might want to just try and run the fuel pump in high voltage mode just to see if it happens. Won't hurt. Just don't leave it in high voltage mode for a long time.