I have a 1991 F250 with the 351W motor. It had a consistent High Idle issue but I took it in to a mech to have them due the major service so they replaced the IAC and EGR but now I am getting an intermittent high idle issue...I will start and run fine some times but one in a while it will want to idle around 1100 - 1500 RPM on the initial start. If I let the truck warm up and then restart it will run fine the rest of the day...not sure what is causing this problem...anyone else come across this?

 

It could be the TPS or a vacuum leak.

 

The engine is supposed to idle high at first start when it is cold, similar to what the choke did on pre-EFI.