Crazy engine problem

black98z71 · October 17, 2005

Well, after fighting a high idle problem for a few weeks and replacing the IAC valve as recommended by the mechanic, I finally replaced my PCM hoping it was causing the high idle b/c that was what he recommended. Well w/the new PCM in, the first time I drove it did the exact same thing...after 5-10 minutes of driving it started revving itself up and not coming down. It would accelerate on its own and at lights would idle at 2500 in park and drive. Well, I was fed up and remebered that some ppl. said that a bad coolant temperature sensor could cause a high idle, so I went and got one at Autozone, but when I went to replace it, it looked different so I was out of luck there.

So, I decided to just unplud the temp sensor and drive it, and coincidently or not, the idle problem fixed itself somewhat. I plugged the sensor back in, and what it does now is that after driving a while it does act like the cruise control is on and will hold speed w/o my foot on the gas. It is drivable now, because it doesn't idle bad at lights. Well, I am at a loss as to what to do next...Change the CTS, or any other ideas. I need to get rid of this ghost.

abqchevyman · October 19, 2005

Have you pulled any codes? Replacing parts without pulling codes is like throwing darts at a dart board in the dark and hoping to hit the bullseye.

I have had problems with several vehicles with rusty connections that takes a while to track down.

Pull codes (most parts stores will do for free) and post them here and what they say. After that maybe we can help.

Good luck.

Mike G · October 24, 2005

I was heading down this road with anotehr issue on my truck. Rather than throwing money (rather than darts) at the motor, I just spent the $100 to have my favorite dealership diagnose it. Cost me only an additional $20 when it was all said and done...

--Mike

rjirvine · October 24, 2005

You didn't say what year your truck is. If it has the round throttle body intake, try installing a new gasket between it and the intake manifold. It's very easy. I did this on my 1988 K1500 w/5.7 and it made a HUGE difference.

If you want to troubleshoot this, spray some carb cleaner around the base of the throttle body unit with the engine running , if the speed changes, you've got an intake leak. Let me know if this helps....

black98z71 · October 26, 2005

Thanks ya'll, but it is an electrical problem. The truck has been at Skeeters Auto repair in Houston for a week and they have had every mechanic there look at my truck. Noone can figure it out...they know it is electrical, but can't track it down. Thanks though for everyone's help.