Tried searching about this problems, got mixed parts here and there about different problems with different cars so I figured I'd post, wasn't sure if it should go here, TPI or electronics. 89 Trans am, 305 TPI, 186k.

First off, we're not sure if my idle is too low to begin with, or how to adjust it. In drive after she warms up she sits just past the middle marker between 0-1k, so I'm assuming it's around 500-600.

When she's warming up, everything is fine, she's idling up there above 1k, which from reading alot of posts, I assume is normal when the car is warming up.

When she's warm, my voltage meter jumps back and forth, maybe by one line or so, and in conjunction with that, the RPM jumps a tiny bit, and in conjuction with those, when my lights are on they flicker big time along with anything else ( gauges, interior lights )

We're not sure if the idle is too low thats causing this. Although I think I saw it should be 600 in a post somewhere, or if my alt or battery is on it's way out.

thanks for any help

 

Idle speed sounds about right judging by other TPI cars I've owned. Besides, it's adjusted by the ECM anyway. Can't just turn the idle speed screw and get what you want.

I would first do a quick diagnosis on whether the problem is the alternator or something on the car that's clicking on and off causing the power drain. Just unplug the field coil wire from the alternator (I think it's still just a 2-wire plug-in on the side of the alternator in 89). Unplugging it will deactivate the alternator and you'll be running just off the battery, at least for a short diagnostic test. Voltage will be lower but you'll be looking to see if it's still fluctuating up and down at low idle. If it is, then something else is clicking on and off causing the power drain. If it's steady then I'd begin to suspect an alternator on it's way out.

 

When I'm idling at a stop light, my voltage drops kinda low and I'm not too comfortable with it. My idle is at 550rpm or so judging by the last time I remember datalogging it. As soon as I take off though, or throw it into neutral (jumps to 700-800rpm), the voltage is right where its supposed to be at. I'm pretty sure I'm going to need a new alternator soon enough, but I was also considering raising my idle for the time being.

 

Bring the alt in to be tested. Most parts stores can do it, it only takes a minute, and its usually free.

 

Thanks for the replies guys, I took her over to a parts store, they tested battery and alternator, the guy said my battery was bad and my alternator was constantly trying to keep it charged, well, I got a new battery, and my lights still flicker, not as bad, but they still do. He did say my alternator is making an odd noise. I guess I've got to replace that too?

 

Odd noises from alternators are not good. Sure sign the bearings are on their way out or some other catastrophic failure is imminent. I'd replace it just on general principle.

However, I'd still do the test I recommended, above while you still have the old alternator on the car. Little diagnostic work on old parts never hurts.

Last alternator I had that made noise worked just fine right up until the last time I spun the motor up to 6200. Then the voltage just dropped down to 10V and sat there. I drove it home just a few miles and took a look. Everything LOOKED fine from the outside but the noise had gotten a lot worse and it definitely wasn't charging. I took the alternator off and immediately realized the problem- I had CHUNKS of alternator guts falling out through the vent holes- little pieces of plastic, wire, etc. It was like shaking a box full of broken plates. The guts of the alternator decided to self-destruct at high RPMs. Whoops.