Mr Paul [T-28]

My friend has a mid-90s Mazda Protege that he uses to drive back and forth to law school, and for the past couple of months it will die when coming to a stop and idling for 10 seconds or so. He doesn't know very much about cars, so he had me drive it today and here is what's happening.

It will only die if the air conditioner is on. The idle will start fluctuating between normal idle speed (say ~800) and approx ~300 rpm. It will do this two or three times and then it will just completely die. If the air conditioner is off it doesn't fluxuate or die.

But with the AC off you can *almost* make it die by trying to roll a window down when it is already down, or conversely try to roll a window up when it is already in the up position.

The first thing I thought was the battery is going out, but he already took it autozone to have the battery checked out and they said it was OK. Would a dying alternator cause this? I'm not sure if it would or not, because it has been doing this for a while I would think a crappy alternator would not be able to sustain battery life as long as it has.

Any suggestions?

Reggie

1. I think you are on the right track with the alternator. Have him get the charging system and battery checked at a different shop - say Sears
2. Idle control valve on the fuel injection system could be bad.
3. When the AC kick in usually the ecu is suppose to kick up the rpms- perhaps the signal is not getting to the ecu

Audiboy

But your friends sounds like it has a vacuum leak, causing the low and erratic idle due to it's lean condition. Have him check that first. Then clean the idle control valves as Reggie pointed out, before checking the AC controlled solenoid for the idle increase. Worst comes to worst, grab a screw driver and turn a bleed screw on the TB to increase idle for now. It's an old car, lots of stuff against it for a smooth idle.