First of all, thanks in advance to anybody who takes the time to ponder my dilemma. So, I own rusty, trusty red 1990 F150 Xlt Lariat 4x4, built with the gas guzzling 5.8L EFI V-8 and E4OD 4 speed Trans. and I think almost all of the factory packages and roughly 110,000 miles. My question is, why does she idle fine when cold at about 800-1000 rpm, But while she's warming up and I give her some juice she wont come back down any further than 1500 rpm., and won't rev down to the normal range until I shut the engine off and then restart. What do you guys think the problem and solution could be. I was told by PO that there is a ADS SUPERCHIP installed by the owner before him, the sticker in the back window further backs up his story, but have I haven't taken out the EEC to be 100% sure.. Would the superchip be the culprit of the high idle, for better throttle response and such? Or Could it be the TPS or other sensors?

 

Check your throttle position sensor, idle air control valve, throttle body, and your throttle linkages. Before you check your tps I would check all the other parts for cleanliness or build up. It could be something as simple as gunked up or worn out throttle linkages but I would think it's more along the lines of a dirty or faulty idle air control valve.

 

Thanks for the input i'll check that tomorrow and let you know if its the problem

 

It was the tps truck runs like champ and ides at 800rpm