i have a 1990 s5 gtu. when i turn the ac on my cars rpms drop so low my car almost shuts off. i can drive city with it as long as i have my clutch pushed in when the engine rpms drop down tho it'll still come close to shutting off. if i just put it in neutral the engine will die. i checked my tps and its fine so i know thats not the problem. what else could it be that makes it drop? i know the car should be able to run fine with ac while city driving! help me out plox!

 

The BAC is supposed to adjust the RPMs to compensate for the a/c, p/s, etc. They put a load on the engine and the ECU compensates with the BAC. So I'd start with the FSM tests for the BAC.

Good luck

 

well it looks like someone fucked with my tps screw so after i fixed it again that did solve the issue a lil bit but it still goes down quite a bit. not as bad tho!

 

Like vrracing says, check the BAC valve according to the factory service manual. Also check the alternator output and the battery.