Iac

[garyda]

Got a 1990 Lumina 3.1 that blows black smoke sometimes when started.
Could this be the idle air control? What is the difference between this and the idle control motor? I saw both of these listed at Autozone. Should I replace both of them???

[Kooterskkar]

Black smoke when started, could be bad rings, or worn valve stem seals. The IAC only controls the engine speed when the car idles, it has nothing to do with starting the car. If you nail the gas, let it rev up fairly high then let off, do you get a good puff of black smoke out the exhuast? If so its worn rings, not much you can do about that unless you plan on spendin alot of money.

[300+]

Blue smoke is oil - black is too rich.

[Kooterskkar]

Thats right... Arrgghhhh, what the hell was I thinkin!?! Forget what I said about fried rings. Had a brain-fart or something when I wrote that.
Anyways, just what 300+ said, youre probably just runnin rich.

[jeffcoslacker]

Rich on start-up is unusual for these, usually they get lean from throttle plate deposits holding the plate open, etc. Have seen bad coolant or air temp sensors cause this. If the ECM thinks the ambient air is colder than it is, an abnormally rich start-up mix will be set.

[jeffcoslacker]

Or, sometimes a leaking injector, or a fuel pressure regulaotor allowing rail pressure too high can cause fuel to be squeezed into the motor while sitting for a period of time. Then the blow-off when started would produce sooty exhaust.