High idle revisited.

Has anyone ever come up with a concrete explaination for the intermitent high idle? Every once and a while my 4.0 will wind up to about 3000 RPM's, it dosen't stop untill I shut it off for a little while or disconnect the TPS. The TPS is new (replaced it because of this problem) The IAC has been cleaned and the EGR seems to be functioning properly. I have also done a search on this toppic and have not found anything that has solved my problem. Any ideas? TIA

Neil

Looks like you have an '87. I finally got mine to run right after I cleaned the C101 connector. The "grease" used at the factory turns into something a lot like tar and is a total pain to clean off the connector contacts. In the end, I removed and cleaned each individual contact with solvent. It might be simpler to just eliminate the connector and solder the wires together. This connector was eliminated on later years. It the big one just above the brake booster and is held by a bracket that is attached to the firewall.

I did the C101 about a year ago (pipe cleaners and flux solvent) put new dilectric grease in. Should still be good.

Try disconnecting and reconnecting it a few times and see if that helps. I recently did that when it seemed to be returning to its old habits.

I had this problem and ended up replacing the TPS even though it was new. I have replaced my TPS 3 times and the second one gave me the high idle issues. I took it back to the parts place and asked for another one and even though it had been a couple weeks and I had tossed the reciept they agreed to let me try another one. The intermittent idle problem vanished with the new TPS. I see you've already tried reconnecting it so maybe your new TPS is just plain bad. You should have a one year warranty on it so maybe you can swap it out for another one and see if it helps... Another possibilty would be that your CPS is going bad. Do you ever have a hard time starting it or have you replaced it recently?

Good luck!