So my 1990 f150 5.0 efi has a high idle. Most of the time it idles at 1100 to 1200 rpm. I cleaned the IAC valve. Possibly bad TPS sensor? I thought my throttle was stuck but I doused it in lube and made no difference. Suggestions?

 

You mite check for a vac. leak before throwin' parts at it.I had the same thing awhile back,turned out it was the intake man. gasket. I would also get a volt meter and do some testing on the TPS before you buy another one.There are alot of items that send to the computer concerning idle speed. pull some codes too.

 

Great suggestions from toby tough. Before going too far, need to ask how long this has been happening? Any parts changed before or other service work?

I also suggest to remove the connector to the IAC, see if the engine idles down. If it does you most likely have a sensor issue. If it remains high start looking for vacuum leaks.

 

[quote=rla2005;11315118]Great suggestions from toby tough. Before going too far, need to ask how long this has been happening? Any parts changed before or other service work?

I had my truck in the shop in October because after they replaced my starter, my throttle kept getting stuck open. They diagnosed it as needing a new throttle body. I'm going to do that repair when I can track down that part but they doused it with lube which i have also done which let the truck idle around 800 rpm. In December, it had problems idling consistently but I cleaned the IAC valve and that solved it but now the truck just idles high and cleaning the IAC valve didn't help. I know I need a new throttle body but this problem is just at idle.....

 

I also replaced the vacuum canister on the passenger side (coffee can) with a non rusted out one

 

Mine did this when the TPS went bad, didn't throw a code, not sure how to diagnose this. I had a local shop figure it out and hell they put an IAC on first. I imagine the TPS would show voltage out of range from where it's suposed to.

Hope this helps some.

 

Fuel Injection Technical Library » Throttle Position Sensor (TPS)