Pontiac Repair: Ac/Heater, electric cooling fan, pontiac firebird

Question
QUESTION: I have a 91' Pontiac firebird 3.1L , for a while now when I turn on the heater or a/c the car runs really rough and tries to quit. I dont know what the problem is. sometimes I can turn it on but I have to leave the fan on low, any higher and the car starts to run rough again.

ANSWER: Hey chris:
sorry for the delay I just got this question today 11/16 it was in the question pool for some reason and I fihed it out. well it could be a few things you could have a vacuum leak inside the hvac control head or one of the acatuators and it is robbing the engine of vacuum. You would hear a hissing nois from inside the dash somehere. It could be you have a chagring system issue with this car and the higher fan speed is dropping the battery voltage lower. Not likely but a possibility. Lastly if you turn on the A/C or the deforoster the A/C compressor is running and that extra load on the engine is making it want to die. WHY? you could have an idle control motor that is acting up or carboned up or you could have an engine throttle plate and bore that is dirty with carbon causing you problem. Just a few things to check with out seeing this it's hard to say exactly the issue is. Good luck :)


---------- FOLLOW-UP ----------

QUESTION: Basically I have the same problem when the electric cooling fan kicks on for the engine. when the temperature reaches a certain degree the fan automatically comes on to cool the engine. when this happens the engine tries to quit and I have to put it in park and kind of rev it to get it to run correctly. Do you know what this problem could be?

Answer
Hey Chris:

Did you have the electrical system checked? Is the alternator output to where is should be? Another thing I didn't mention is does the fan turn hard? with the engine cold and the key off does the fan blade turn hard? there me be excessive draw from the fan putting a load on the electrical system. In most cases it would blow the fuse first but just another thing to look at. Did you try the other couple of things I mentioned? does this car Idle okay all the rest of the time or does it hunt for an idel speed? If it doesn you could have a vacuum leak some where and the extra load on the engine is more the the idle control motor can handle. just a few other Ideas This one is kind of out there as for as far as strange things happening. good luck :)