2000 F150 4.6 170K miles mostly hiway miles.

Stopped in a parking lot a couple weeks ago and put the truck in Park and it went up to 3000 rpm. Managed to limp it home.

Pulled connection off IAC and truck idled down but was undrivable.

Pulled IAC and cleaned with 2+2 thouroughly-no change.

Replaced IAC - problem solved - sort of.

Yeasterday it did it again. I hit the gas hard once and it cleared. It's done it a couple times before this last event but cleared within 30 seconds.

No check engine light
Have not had it scanned yet (tonight)

Have read through several posts on this problem. It seems my options are an O2 sensor (no CEL though), the TPS, or the EGR. There was also a post on getting the processor flashed with new firmware. I'm leaning toward an TPS but am not sure.

Truck is basically maintained. Oil change around every 3k-4k miles. New fuel filter every two years, new air filter every year. Has new plugs and new fuel pump 1 year ago.

Am familure with basic fuel injection and do all my own work. ALways have.

Would like some help with this one as I have $50 in the IAC and really don't want to throw parts at it.

 

I know the autoparts stores don't like it but you could return the IAC if it did not help, depending on how ethical you are (you'll have to lie and say you didn't use it...).

You could check for vaccuum leaks. The PCV hose behind the intake at the elbow likes to rot away, as do the EGR hoses and intake gasket area. 4.6 is known to have fully plugged up EGR ports, you could check them.

Could it be a sticky throttle cable or failing spring on the throttle body maybe?

Those are all free to check.

 

Sounds like a vac leak. I know its not a ford truck, but my buddy had a 97 intrepid, it would drive fine but in neutral or park it revved to 4k turned out being his lower intake gasket.