Hey guys,

I'm trying to get a second opinion before I start pulling and cleaning parts.

My '91 Z28 305 TPI will start clean and idle steady at about 650 according to the tach. in the dash.

However, if I turn the A/C on... or wait long enough for the engine fan to kick on... the idle starts to go bad. It's worse with the A/C on, it starts to lope between 500 and 1K RPMs and sounds like it'll almost stall (but it seems to hang in there on its own). With just the engine fan... the idle range is much smaller, but the surging idle is still there.

From everything I've read on the board about idle issues... I'm thinking it's most likely the IACV (Idle Air control Valve). Since the idle is solid with no accessories running, it seem hard to think it would be a vacuum leak. And since turning on the A/C or other accessories should affect the amount of air allowed in via the IACV (Is that correct???), and that's when the idle goes south, to me that seems the most likely culprit.

Any thoughts, ideas, or corrections to my thinking? Thanks for the help!

 

bump

 

In some cases I have found that cleaning the throttle blades help a lot with this. Open them fully and wipe the throttle ports and back of blades with shop towel and carb cleaner to remove the gunk that builds up behind them.