I have done a search on "idle" and it wasnt working. I also know that there is an irratic idle thread just down the page. However, without knowing what the idle issue is with there and without hijacking that thread......I have an 89 Iroc with the 5.7. The motor was rebuilt by a reputable person just before I got it. I have since put about 35k miles on it with no problems. However, it has recently began idling funny, but only at times. The car fires and runs cold like a new one. At a couple of different speeds thought (40-45 and 60-65) if you barely let off the throttle it will begin to pulsate. Slight touch of gas and it eliminates most to all of it. Also, idle is good at start. Idle is good if you slowly back off the gas as youre coming to a stop. However, if you let of the gas quick and slow with just the break, it will begin to pulse between approximately 1k and 1500. Occasionally it will stall. Again, slight pressure on the gas and it idles fairly well. The only other things that I can think of, connected or not, is that if it has been running and you shut it off and try to immediately start it back, it will not even fire. It will however start perfect in just a few seconds. Again, maybe not connected. I have seen several articles on the AIC and stuff with idle. Is this where I should be looking and could someone give the enginly handicap some beginner details? Im ok with basics, but the sensors and computers are over my head. Thanks in advance, Bob

 

If you have TPI, clean the injectors and throttle body, then do a complete tune-up and service. My `88 Iroc 383 TPI had similar symptoms as yours and are gone after tune and cleaning.