Intermittent High Idle.
 

I am getting a intermittent High idle code (service engine soon light). Sometimes I get it 3 minutes after I start driving, sometimes I can go 25 minutes before it comes on. At first I thought I had a linkage issue, I disconnected the cruse control just to be sure. I check the throttle cable to make sure it was not sticking. I used carb cleaner all around the linkage.

On a fresh start as long as I do not touch the gas the car idles at 850 RPMs. It will do this all day long and not set a code. When I rev the motor up and let it drop down to 1500 RPMs at a normal rate but then it seems to pause at 1500, Then it is like a switch is thrown and drop to about a 1000 RPM then slowly gets back to the 850 RPMs. The reason I do not think its a sticking cable or stick thottlebody is because of the code. If any of that mechanical suff is causing the problem the TPS would just think I had my foot on the gas and it should not set a code. Also the fact it comes and goes rules out vacuum leaks,,,, I think. I also pulled out the IAC motor and found the end was dirty and a bit rusty. Cleaning it has not seemed to help.

When I shift between gears the car does not go below 1500RPMs even if I pause. I think that is when it sets the code.

I guess all that is left is to replace the IAC motor. Any other ideas?

BTW I did just install this motor. its from a 2002 but the intake and Thottle body are all from the original motor.

What is the code???

Take off your nifty new intake plenum. With the engine running, hold a finger over the small opening in the TB that's right in front of the throttle blade. If your idle comes back down and evens out, your IAC is bad.

Thanks, I need to change the display on my scanner today, for some reason it did not give me a code number. 69 I can try that the only problem is most of the time its a issue is when I am driving. I have had it happen while sitting but most of the time it work ok with the car not running out on the road.

The old 2.8 used to have a problem with there TB binding up. There was a kit to fix that. Anyone heard anything like that with the 3.8.

Well I put 60 Miles on it today and no Check engine light. I am hopeing the choke cleaner I put in yesterday did something. I also pulled the IAC motor and cleaned that. It still seems to come down in RPMs slowly but I am new the 3.8/5 speeds. It does allways seem to get back to the 850 RPMs.

It set today, Its P0507

I'm curious if it's a vacuum leak.

some good info:
http://www.obd-codes.com/p0507

Thanks for that link. My first thought was Vacuum. But at this point I can go out and start the car and let it idle all day and it will not set the code. I would think a vacuum leak would be at its worst at idle. It only sets the code while driving. Since both the EGR and the PVC work under light load and " turn off" when going to idle I am going to start there.