Looking for help on my 1991 F150. It has the 5.0l 302ci engine with a standard 5 speed and is a 4X4. I bought this truck and when I got it home I noticed that the connector going to the IAC valve was disconnected. The truck has been running rich and not wanting to idle when it is first started. After it warms up it runs OK but not great. It will back fire between shifts and the check engine light will come on periodically but resets when I turn the truck off and back on. The issue I have is that when I hook up the connector to the IAC valve the idle goes from 900 RPM up to 2500 RPM and setting the idle screw all the way out makes no difference. The truck runs much better when the IAC valve is plugged in. The back fire between shifts goes away, the truck doesn't run rich anymore and the check engine light stays off. I just can't get the idle to go below 2500 RPM when the IAC valve is connected. I have replaced the IAC valve with no change. I also replaced the cap , rotor, plugs and plug wires. I'm not sure where to go next with this. Any suggestions????

 

hook it up and adjust your timimg

 

OK. Thanks I will give it another shot. I did give that a try and it seemed that when I got the timing set then the truck didn't seem to have any power. I will give it another shot and verify that I have the correct setting for the timing. Thanks again!

 

Error code scans!

 

first of all STOP MESSING WITH THE IDLE SCREW....

you set that with the IAC unplugged....period...base idle with IAC unhooked then plug it in...

if it fast idles that usually means the 2-wire temp sensor next to the thermostat is BAD....