Idle issues ~ alt belt is related
 

So my 83 gsl has been giving me a few issues lately. Alt belt is chirping at high RPMs. Obvious solution is to tighten down the belt in my mind. I get it tightened to the proper deflection and get it running. The car starts idling really rough and chokes on me if the belt is tight enough. With gas it is fine, but the car feels slightly less responsive when I give it gas. Loosen it just a fraction and the idle issues go away, but the belt chirp is back at about 3500+ rpm. This is really repeatable, I can tighten and loosen it to get either chirping or idle issues. The alt is charging happily, I have had no issues in that regard, and the battery is healthy.

One of things I could see it being is a bad bearing in the alt, although the chirp is definitely the belt, not the bearings. You can see it wobble at high RPMs. Only other thing on that system is the coolant pump if I understand things correctly. I have no indication that anything in the cooling system is working incorrectly, but I can't rule it out.

I don't know what would make it idle hard in that system and I am hoping you guys can shed some light on this issue.

When you tighten it down it may be too tight and thats causing issues with your idle. The
chirping is a common problem, but usually up around 5 or 6K rpm. Solution is dual belts or
move the alternator to get a better wrap in the waterpump. Also making the belt too tight
can lead to accelerated wear on the eshaft bearings, so be careful not to over tighten the belt.

I would have the alternator tested to see if its putting out at spec and also to see if it has a
wobble or not. Sounds to me like an alternator issue. Maybe its always engaged. Is your
battery good and staying charged? A bad battery can force and alternator to run constantly
to compensate for it.

Yeah, my belt used to only chirp at 6k or so, now it does it at highway speeds. More of a constant whine then a chirp honestly. I am able to keep the belt tight enough that it doesn't chirp at a low rpm transition, or when I give it more gas to accelerate quickly. I am fairly sure the battery is good. I can play the radio for a while with the car off and the car starts right up and the battery never seems to be losing a charge. It's a bit hard to tell the health of the battery (for me) because it's a daily driver and it never really sits.

My alt seems to be running when ever the engine is, the voltage dial on the dash is always at ~13.5. I was under the impression that was normal. I can easily have the alternator tested at a local shop to see if it has issues.

Moving the alt sounds like a serious mod, and may be beyond my abilities. Dual belts I assume use that dual pulley I have seen for the alt, but where does the other belt go to connect to the engine? The pulley for ac power or something? I can look that up once I have more time this evening.

I had an alternator bearing fail on my 91 Camaro once. Stopped the car dead in it's tracks, right in the middle of rush hour on the Hollywood Freeway. Locked up so tight the starter couldn't even spin the engine - - I thought for sure the engine had seized. Had to get towed off the freeway.

That system used a serpentine belt with a spring tensioner - - our older style v-belts are more likely to slip, or break - - but it's clear proof that the drag of a failing alt bearing can be enough to stall a car, which means it can be more than enough to mess with idle smoothness.

Probably looking at a new alternator unfortunately. Good peace of mind on a daily driver before it fails like Divin mentioned.

The dual alt pully is used if the stock air pump has been removed. If your air pump is still there, you can't really use the dual pulley. The dual pulley is used to eliminate belt noise on the waterpump when the air pump is removed so it's use is unrelated to your issue.

i had an alternator lock up on my 83 Rx7, it gave tons of warning, the bearings were obviously bad for a long time, but anyways one day it locked up approaching a red light, although since its a mazda by the time the light turned green, it was fine, and i made it to work and back home....

so i'd spin the alternator over without the belt, it should feel heavy but spin smoothly. the water pump should also spin freely, and not have any side to side play. this same 83 had a bad water pump, it didn't leak a drop but it had an inch of side to side play! made a hell of a noise too

Same here. Had an alternator lock up. Starter worked it's butt off to get one revolution. I thought the starter and battery were dead at first. Finally push started it, and the belt smoked big time, but ran. That's when I found the alternator wouldn't turn.