92 f150 302. I had a idle surge problem pretty bad, but I fixed a vacuum leak and replaced my tps. Check engine light went off and it runs much better. However I still have idle surge, but only if I let my truck idle for a little bit or if I let it sit at idle when I start it up. If I start it up and just take off I have NO idle surge. So any ideas what this could be?

 

Idle lope...vacuum leak.

No codes now? Run Key On, Engine Running test. How's the PCV valve? Pull the PCV valve and with engine idling, take a sheet of paper, and allow it to block flow off. Does the idle lope quit? Vacuum leak.

 

I will try that. Could it be idle air control valve?

 

Not necessarily. The IAC valve tries to control for a steady idle or to increase say for turning or Air conditioning compressor. I would double check ALL vacuum lines and inspect both vacuum reservoirs.

Edit: A non functioning IAC would result in low idle/stalling condition.