Engine seems to think gas pedal pressed when it is not

  • 150,000 MILES
My car (CE V6 automatic) has two distinct behaviors and both tie in some form or manner to the idle speed of the car when at operating temperature. That is when I know the car will have a problem or not when I drive it - the idle speed is either normal or not. And switching between the two conditions I will describe below is completely random, but the description in 2 below seems to happen more and more often.

1. When idle is normal (around 650rpm in N or P) - shifting from N or P into R or D is normal. Driving is normal too.
2. When the car idles - for no apparent reason - higher than normal (in N or P), and sometimes over 1000rpm, I observe the following:
a) Shifting from N or P into R or D is very rough and the car gets quite a jolt when the gearbox engages.
b) When driving open road and I take my foot off the gas, the engine refs do not drop the usual approx 300rpm, but stays at the same rpm as if I have my foot on the gas pedal. The car does not really slow down either as it would normally do - it keeps on going.
c) at some point the engine check light was on for about 2 weeks and then went out again. Has not come on since.

And then randomly the condition in 2 above will disappear and all is normal again.

I took the car to a repair shop and they could replicate the problem. They also confirmed that the accelerator cable does not stick at all. They also found an error related to the TPS in the computer's memory (the engine check light went off on my way to the repair shop). They could not with certainty say that it is the TPS.

The gearbox's behavior seems to be related in some way to the faulty idle speed.

Any advice will be appreciated.
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Wednesday, November 23rd, 2011 AT 12:33 AM

1 Reply

I was going to suggest testing the Throttle Position Sensor as it can be tested for voltage calues at min and max throttle, which does not take long. However, it may not be adjustable, if it is you can try to bring it in to spec, if you can't bring it into spec it needs to be replaced.
I would double check the butterfly valve on the throttle body as that is where crabon type deposits collect. They can keep the butterfly from closing all the way but can also block the area that it is collecting in which kind of blocks the air flow and will make it intermittant. If it is dirty. You might want to remove the throttle body and clean it with craberator cleaner and a rag and/or paper towels. When cleaning ports, always shoot the cleaner from the outside in towwards the intake as doing the opposite may clog any deposits further into port.
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Wednesday, November 23rd, 2011 AT 12:43 AM

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