Alright, I am looking for the next thing to check to solve then high idle problem my 2001 f150, 5.4L, AT, 4x4 truck with 288k miles is having. The truck idles (even at operating temp) at 1000 RPM.

Due to a coolant leak, the plastic intake was replaced with a Dorman. Meanwhile there were new plugs, COP's installed and the fuel injectors were checked and cleaned. The idle was high then so a whole can of carb cleaner was used to try and locate a vacuum leak! No leak. Smoke test, no leak. The throttle body was cleaned spotless, MAF sensor was cleaned/tested (voltmeter), new IAC valve, new fuel filter and fuel pressure was tested at 40PSI at the rail and 80-90PSI post filter. Still high idle. SO, a new fuel pressure regulator, vacuum hoses/elbows, checked brake booster for leaks, nope, another can of carb cleaner and Still high idle. What next?

The only codes I have (which came later) are lean banks and the pre-cat O2 sensors will be tested or replaced in the near future.

IDEAS??????

 

Please post the exact numeric codes.

Have you checked the PCV elbow behind the throttle body? That's the most common vacuum leak, you need to physically check it, stop spraying carb cleaner - that in itself is really rough on rubber hoses.

 

codes p0171 and p0174. all elbows, especially the PCV were replaced or are new.

 

Lean codes both banks is either unmetered air after the MAF (vacuum or intake pipe leak) or fuel starvation (clogged fuel filter, low fuel pressure, clogged injectors). With the high idle, my money is on an intake leak.

 

I have had this issue and it was a leak after my MAF but I am having this same issue but no codes on a different truck and I've done all the checks. I recently got a P1451 code for the evap canister if I remember correctly.

 

Good point - you need to chase the evap line back from the manifold - it may be busted somewhere and sucking air. That's a pretty big hose. Same with the power brake booster hose.

 

I've seen it before.
It's likely the Dorman intake install.
Either the intake does not fit all the ports or it's the intake gaskets used.
Good luck.

 

Another good point - you HAVE to use the Dorman gaskets, you can't use stock gaskets.