In short, here's the problem: My '82 K-Jet has trouble idling. When WARM, it stumbles, and even stalls. When the throttle is open, everything is fine.

HERE'S THE THING: When I turn the A/C on, it idles as smooth as buttaaa! Never stalls or stumbles! What could the A/C have to do with the idle? I know that turning on the A/C raises the idle speed a tiny bit, but there must be something more.

Is there anything vacuum related with the A/C?

Could the A/C affect a sticking IAC?

What about this vacuum check valve, could that have something to do with it?

Note 1: When the A/C is off, and the car stumbles or stalls at idle, I hear a hiss coming from under the dash(?) right as the revs drop.

Note 2: See Sirmebes' recent posting about his idle problem if you want to know more details about the symptoms of my idle problem and what I've done to try and fix it. It seems like we have the same symptoms, and have attempt the same cures.

Also, is OK to drive around with the A/C on ALL THE TIME?

even my mechanic agrees with it. Pinholes in the intake system will become a problem only when the engine is warm due to the fact that warmer air is 'thinner'

I tell ya, it's a bloody pain in the arse when you are looking for a pinhole sized leak! I've been at it for weeks and wife's just about it had it with me screwing around....with the car that is :-)
My next course of action is to replace all the vaccum tubes and any related to intake. I did try spraying carb cleaner around each injector and around the TB, but no change in RPM.

Good luck, and if you do find a solution, be sure to email me.

SM
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90 BMW 325is, 98 BMW 528i, 90 Volvo 240DL

I am thinking, why would your run better with A/C on....what changes...well, for one, the engine is under load, hence it demands more fuel and air than when it idles.

You know, it could be as simple as re-adjusting the throttle switch, which I have yet to check. It might just be bad or just on ethe verge of being either on or off.

Either way, I will let you know by email tomorrow.

Cheers,
SM
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90 BMW 325is, 98 BMW 528i, 90 Volvo 240DL

Have you checked the hoses to and from the Idle valve? Mine were split causing idle troubles. Checked the large rubber bellowes that connects the fuel distributor to the intake? Clamps tight? Does adjusting your idle screw make any difference? I would also check all your connections under the dash, all the flaps that direct air flow under there are vaccuum controlled. Make sure none have popped off. Don't think the check valve is the trouble unless its cracked and causing a vac leak. The idle is dependent on the amount of air bypassing the throttle body, so any unmetered/extra air is going to cause trouble. Good Luck///
Chuck
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Chuck Jaxel, Pine Hill NJ, Near Philly...

YEAR?

Its a 1982 with a K-Jet B21.

I grabbed a junk yard IAC yesterday, but it was junk. Only made it worse.

I really think the IAC is sticking when it gets hot, but I still don't understand how the A/C would affect that?