'91 GM - erratic idle

[monterey1962]

Erratic idle started up a week ago when this frigid weather started. No real pattern to it, just happens every now and then. I've put on a new IAC valve, reset the ECM, and cleaned the throttle body. Still has the erratic idle. I turned the throttle adjustment screw up 1/2 a turn. Went over the vacuum lines, too. Didn't pull codes. Too damn cold out.

Can someone remind me ... when you unplug the IAC sensor wires, what is the car supposed to do? Stumble? When I unplug it, the idle does not change.

[marquisman]

im pretty sure its suposed to stumble

[monterey1962]

Put the code reader on. Only two codes come up for thermactor errors (emissions system is disconnected), otherwise it's clear. I'm thinkin' it has something to do with the cold weather 'cause it ran great when it was nicer out. Either way, I'll just drive it this way.

[86VickyLX]

when you unplug the IAC sensor wires, what is the car supposed to do? Stumble? When I unplug it, the idle does not change.

it supposed to stumble and die.

[gadget73]

If the screw is set too far up, it won't die. It should if the throttle stop is set properly, and the IAC is good though.