Ok so lately I've noticed that if I drive a long distance on the interstate (a couple hours at least) with the A/C on or the defrost on (which involved the compressor kicking on and off), the engine is hard to start again after it is turned off. It will fire, die immediately. It takes a good 6-10 tries before it will finally stay running. If I keep my foot on the gas during these tries, it will stay running, but as soon as i take it off it dies. Once it stays running, it runs great! This problem ONLY happens if the air or defrost is on. If i drive long distances on the interstate with out either of those two options on, it will start back up just fine. Any ideas? The engine is a 5.9L v8 and the truck is a 1994 with 140,000 miles on it. Spark plugs have been replaced as well as the fuel pump and all parts associated with it back in 2007. Thank guys, this is also my first post here so thanks for reading!

Josh

 

I'd replace the IAC, and clean the bore it goes into on back of the throttle body. Hell, remove the whole TB and the sensors on it,and clean the whole thing. And while it's off, use a flashlight and mirror and inspect the inside of the intake manifold for any oil pooling.