JAFO1994

I've pretty much replaced everything or checked out everything except the opti on fixing my rough idle. First all it's only in open loop (warmed up). I disconnected the MAF and it idled perfect which lead me to believe it's my ported MAF. But I notice that when my AC is 'on' it also idles smooth, but it doesn't idle higher with the AC on or when it cycles. Every other car I know of with AC on raises the idle to compensate for the drag of the AC compressor on. My questions are; does the LT1 suppose to raise idle when the AC goes on? Why does it idle smooth with AC on, but rough when turned off? I was thinking perhaps my idle screw was turned out too far and the computor was fighting to lower the idle rpms but when the AC was turned on it was happy so to say. I've never touched the idle screw, but the past owner could have. Any thoughts or suggestion. I was going to start playing with the idle screw as a last resort.

Injuneer

The idle is controlled by the PCM, using the IAC motor to alter the amount of "idle" air that bypasses the throttle blades. When you turn the A/C on, the PCM simply increases the IAC setting to keep the idle exactly at the no-A/C level. You shouldn't see any more than a tiny "blip" in RPM as the A/C cycles on and off.

You need to get a scanner on it, and see what your IAC control motor is doing in response to changes in idle speed. Perhaps the IAC motor pintle, or the idle air passage is crudded up, making it difficult for the valve to control correctly. Or it may be "bottoming out" at 0 counts when trying to control the no A/C idle, but need to stay open a ways to meet the higher demand of A/C idle. You need to scan it.

Not sure what you mean when you say:

The engine starts cold in open loop, goes into closed loop when the coolant warms up and the O2 sensors start to function.

JAFO1994

Not sure what you mean when you say:



The engine starts cold in open loop, goes into closed loop when the coolant warms up and the O2 sensors start to function. [/B][/QUOTE]

Opps, meant closed loop. It idles great when started up warm for the first few minutes, then start's to idle rough. I believe even when the car is started up at operating temperature it's in open loop for the first few minutes then goes to closed loop, this is when it idles rough.