I'm having a problem where if I put the AC on, the idle drops down to like 500 or so, and almost cuts off. It stays running barely, and at 500 the idle sounds pretty badass, but whats wrong?

 

You probably aren't getting enough air at idle. It can really be a problem with aftermarket throttle bodies as the problem isn't as easy to fix as with a stocker. You can try to open the blades a little more with the TB screw, if that doesn't work you may have to try one of the IAC mods.

 

I have the same exact problem. I stopped using the ac.

 

This worked on mine. The aftermarket T Bodies arent designed like GM's, so open the blades alittle to get the extra air in. There are several other ways too, ie drill hole through center of T Body between blades, or little holes in the blades.

 

If you are running a stock TB you just need to drill out the hole in between the TB blades. The size most people use could probably be found in a search.

 

Wouldn't that cause my idle to be higher with the AC off? It's fine with the AC off, idles where it's supposed too. When I put the AC on it dropps 500 rpm or so. I really don't use the AC anyways, but it'd be nice to know it works fine if I need it...

 

Well i say crack your TB blades some more. If you can't do a search under my name and IAC mods you should find another way to fix it.

 

When you turn the AC on the IAC is going to max, so compensate by opening the bladesa little. Just turn them open enough not to raise the idle. You should have room for that. Make sure the car is warmed up.

 

A/C is ugly and makes for a cluttered engine compartment...just yank it

 

The only thing I can think of is the vacuum lines inside the cockpit may have a leak. But if that were the case you might have the symptom of when you jump on the throttle, the air coming out of the ducts appears to stop until the engine speed levels off again. Then the air begins to blow out the vents again. Did you notice that?

Take a look at the vacuum check valve on the firewall near the PCM. See if it's damaged at all. there should be 3 hoses on it. Remove and plug the one that goes into the firewall both at the hose and the check valve. Now turn the AC and see what happens to the idle quality.

 

What is th efix for AC on making car run like crap and want to stall with big cams. IACS where (what numbers. AC on and off), TPS voltage need readjusting afterwards?

 

If you have access to a scan tool, verify that the IAC is wide open (or close to it) with the AC on. Maybe the IAC is sticking.

Instead of drilling a direct bypass hole, has anyone tried porting out the IAC passages in the TB for more flow?

 

It can't really be done on aftermarket TB's which is where most of us have the problems. If you have a stocker drill the hole out and be done with it.

 

My Tbody has all the mods to cure this and the BLM issue.
But what does loweirng or raising the voltage do to the pcm, does it add or lower fuel when the voltage goes up or down. When I turn mine to lower or raise, the idle is definitely going up and down. I elongated my TPS to allow adjustment.

 

I realize this thread is a little old, but I just ran into this problem and I think the information here could be a little misleading. If your engine idles fine and only drops when the A/C is turned on you could just have a bad IAC valve. If the valve doesn't move it can't allow in any more air to help maintain the proper idle speed.

I pulled my IAC valve out of the throttle body and cycled the ignition a few times to verify the old one did not work. I bough a new one and verified that it indeed moved when the iginiton was cycled. I installed it and now the idle stays the same even when the A/C is turned on.