1991 Chevrolet Cheyenne Idle air control valve

WIZARD505

MEMBER
1991 CHEVROLET CHEYENNE
5.7L
V8
4WD
MANUAL
165,000 MILES

When I start my truck it idles fine and then all of the sudden the idle air control valve will cut out and start running sluggish like it wants to die out and black smoke starts coming out the muffler then after I rev the engine a couple of times it stops. Then it will run good again then all the sudden it does it again I replaced the idle air control valve with new one and it still does it some days it will be doing fine and then out of nowhere it does it again I replaced all parts on throttle body any idea why the idle air control valve would cut off and cut on. Thank you

2 Replies

WRENCHTECH

MECHANIC
20,761 POSTS

You don't have an IAC problem. Your engine is getting overloaded with fuel for some reason.

You can look at the injectors when the engine is first shut off to see if any fuel is leaking out of them. If not, then it may have a fuel pressure regulator with a torn diaphragm allowing fuel to leak through. Unfortunately on the TBI engine the regulator is not accessible externally so you may have to try a different throttle body to find out. Another way is to use a fuel pressure gauge and see if the system hold rest pressure. If it doesn't, that would be an indicator of a possible leaking regulator.