My 88 f150 with a 302. Is still having idling issues when the motor is cold. When you start it up when the motors cold it idles up to where it should then a few seconds later it drops. It drops so low that it almost stalls out then the idle shoots up again. It will keep doing that until the motor warms up. Sometimes it goes down so low that it will stall out.I replaced the idle air control and the idle positioning sensor. Any ideas.

Thanks
Tim

 

Have you tested for fuel pressure yet? Is it do that while driving or at a stop? Also when you replaced the IAC, did you clean/ replace the bypass spacer behind it if it is equipped with one or the air ports? If its got crud in it, that will also cause idle fluctuations and stalls when cold.

 

maybe this

 

I already put on a brand new idle air control.

 

No my doesn't have a spacer. The truck doesn't do it at all after it is warmed up.

 

Have you tried to clean the throttle body, replace the Throttle position sensor i have had this problem with my 4.9l in my 90 and also the same problem with my 4.2l in my 99 and that has fixed it.

 

TPS....clean or replace

 

Have you checked for codes. Could be the air charge temp sensor or coolant temp sensor (not sending unit).

 

You might have replaced the IAC, but did you clean the air ports to it? If the ports that it bolts onto has crud in it, its preety much usless. Also check for codes. And when you replaced your TPS, was it set to the same as your old one was?

 

When I replaced the tps it was in the same place as the old one. Can you change it? That's why I replaced the old because the truck was doing the same thing.