S5 A/C Idle Issue
 

I have a 91 vert that idles great even at 750 but once I switch the A/C on or if I have alot of things going such as the lights, fog lights etc.. the idle will dip as well.

When I turn on the A/C though it will just about kill the car if not kill it at times. There are a few times where the idle will go up like it should but 8 out of 10 times the idle drops.

I have checked for vacuum leaks, checked the BAC valve according to the FSM and it is within spec. I have the idle between around 800-850 rpm as the TPS is sitting right at 1 dcv.

What else could cause this drop in idle?

Thanks!

1) intake vacuum leak

2) alternator cannot handle the load


-Ted

Thanks Ted

Looks like it could be the alternator which I should have checked before anyways. I show it to be putting out about 13.5v but once I turn on the A/C, lights, brights and radio it falls down to 13v and below as it pulses. Once I turned everything back off the alternator is now only putting out about 13v to alittle below that.

Idle is right on 750 as well.

Thanks!