1993 C4 Six speed w/c68 ac. Car was running fine until I turned on ac. Ran rough add would die. Reset computer by disconnecting battery. Would start after cranking long enough for fuel pump to on, but as I turned on headlights would act up again and lights were very dim and would not rotate. When light switch on, throttle cable on top of intake would get hot as it was acting like a ground. Some ideas?

 

I would pull the battery connections check all connections and grounds and cables make sure all are good tight and clean. The pump should run for two seconds when you turn the key from off to on without starting.

 

One way or another any low voltage to the ECM and other sensors will cause an assortment of problems. Might also consider the battery itself as a problem. If no SYS light the battery may be OK.

I would definitely check the battery connections, both ends and major grounds including engine to chassis. Make some measurements with a DVM to get a better handle on the voltage problem.

 

Hi there. Next time you're out there running it, can you tell us what the voltage meter on the dash is reading without any current loads (no headlights, no ac), and then can you tell us what the meter does when you turn those devices on with the car running? Even if you have to give it gas to keep it alive, those readings can be a big help. Your alternator should keep the voltage around 14.1 volts when running, even with accessories on. A serious drop in voltage that doesn't recover can be an indicator that the voltage regulator in the alternator is failing, or the alternator's field coils are not being energized properly, or there is a problem with the alternator connection to the battery. If available voltage gets too low, the ignition coil won't have enough juice to create a strong enough field to fire the secondary winding, resulting in poor spark and rough running conditions. Additionally the fuel injectors may be affected too.

Before I start rambling, what I'm trying to say is that it sounds like your car's charging system is not working like it should. I think you should check that first. A faulty regulator, or a diode in the diode trio can cause problems. A failed diode will allow it to charge, but not as fast as it could/should, which can cause problems when electric accessories are activated but not display any symptoms when they are off. Good luck with it!

 

A hot throttle cable is a definite sign of a bad ground connection between the engine block and the battery!