Guys maybe one of you can help me out. I have a 1991 f150 Lariat. I had a new motor put in it and it runs great. However I am having two issues.
1. When I start the truck up after it is warm, it first idles to 2K RPM and then comes down.
2. When its cold it doesnt idle so much but it does go up close to that high and then comes back down.

BACKGROUND: When I bought the truck the pollution pump had been taken out. The houses that ran to the pollution pump had been removed and those vacumes that were left over were capped. So pretty much the only thing left on the truck as far as pollution parts are the 02 sensor, egr valve, travel position control switch and maybe a few others.

Now I dont care too much for re-installing all the pollution stuff since here in Florida there is no pollution control whatsoever.

My question to you is this. Is there anyway to modify the computer on the truck so that its not checking the sensors on the engine for feedback, which i think is whats causing high idles on startup, without have to remove the computer and everything and go carburated???? So basically I looking to fix the problem with the idle on startup... Any suggestions woudl be great...

 

O2 sensor is vital for the motor's operation, do NOT remove this. EGR helps to lower NOx levels at cruise speeds and reduce combustion temps, this is good until you get a cam that self EGRs. Until you get to that point, leave EGR.

Cold start is normal to idle high then come down, think of a choke on a carb'd vehicle.

Do you have a tach where you're viewing these RPMs at a warm start? How long does this last... if it's for a few seconds it's pretty normal of open loop computer operation.

 

Sounds like you have a vacuum leak. Spray carb cleaner around the intake manifold and all the hoses. If the rpms increase, you found a leak. Typical symptoms of an air leak.

Robbie