i recently replaced my tps and cleaned the iac and throttle body and now my truck idles at 1100 rpms or so. truck is a 94 f150 5.0. any tips on what to do to get it to idle lower?

 

I would check for vacuum leaks. I would also go to fordfuelinjection.com and click on TPS and adjust the new TPS to get the recommended voltage as specified.

 

at the same time i changed the tps and cleaned the TB i also replaced the pcv valve. i have adjusted the tps several times and i have gotten it to idle a little lower but is still too high. at first startup it will run at roughly 1300 rpms then after a little while it will drop down to 1000-900rpms. i have also significantly lost fuel mileage. haven't been able to find any vacuum leaks so far either. any suggestions?

 

Use a hand held vacuum pump/gauge to test each vacuum circuit/component. My '92 F350 passed all the spray carb. cleaner on the hoses/intakes tests I could throw at it but it still idled similar to yours. Once I used the vacuum pump/gauge I found numerous hoses were faulty as well as a rusted through metal vacuum reservoir.

 

Sounds to me like a vacuum leak. The vacuum lines age to a brittle state and when disturbed by working on the engine you can easily fracture them.

If that checks out okay (with a gauge as others have suggested), then I would check the IAC valve that's mounted on the intake. Sometimes they get clogged up or "stick".

If you're lucky like me, you're truck will eat one every 40-50,000 miles.

 

thanks for the suggestions. i will check out the vacuum lines in the next few days. hopefully this cold weather will get out of here. and the iac appears to be new. the previous owner must have changed it not long before i got it. it looks brand new and i cleaned it out when i had the TB off. if i unplug the iac the rpms do change so apparently it is working

 

i checked all of the vacuum lines that i could get to as well as the vacuum can and all checked out fine. tps is set to 0.940V at closed throttle and still fighting the high idle

 

Did you remove the TB butterflies? When I gave my TB a really good scrub down I didn't get them in properly and it had a higher idle. Not sure how much, as I lack a tach.

Loosening both valves off and playing with the throttle arm got them centered and I torqued them down again.

 

no i did not remove the blades. just held them open and sprayed everything down good with throttlebody cleaner until it was good and clean

 

pulled codes today. koeo test resulted in these codes 332 and 558. koer test resulted in 332, 411 and 538.

 

i can unplug the iac and it idles pretty good. in the 750-800 range. does that mean that the iac is bad?

 

is there a spring on your tps? when i replaced the one on my xterra i happened to not upt it in exactly right and it idled high.. I adjusted it and it ran fine after that. just a thought

 

a spring? i want to say there is a spring built in it. but not one on the outside

 

yes the one on the inside.. i had put the little nub ( i have no idea what to call it) on the wrong side of the linkage in my xterra.. i reversed it and now it runs great...sorry for the vagueness..lol

 

i'm pretty sure i have it on the right side. otherwise the voltage would be way off correct?