Amperage drop

[SuzukiGhostRider]

Car is an '88 Beretta GT with a '90 3.1L /auto.
I've got a amp problem in the GT. Whenever I put it in gear (Drive or Reverse) the amperage goes from just above half on the guage to just BELOW half. Especially noticeable at night as the lights will dim (headlights and dash) but as soon as I give it just a touch of gas, it goes right back up, of course down again when I let off. I had the battery and alt tested "in car" at Checkers here locally. BOTH tested out good. This problem is actually causing the car to die occasionally after backing up ,then when switching to Drive, car dies. Or sometimes, put it in gear, hit the gas and she dies. I should add I JUST put a brand new Luber Finer fuel filter in it the other day. The old one was flowing but about half strength compared to the new one. This helped SOME ,but not much. I've checked the spark plug wires and they are fine. Will be putting a new set on shortly anyhow. Put new plugs in today. The old ones were gapped around .35. I gapped the new ones PROPERLY at .45. This didn't change my amperage problem at all, but DID help the car run just a bit smoother. Was noticeable to me anyhow, and the old plugs were rusted from sitting. He must have used anti seize though, as they came out easily. And yes, I did on the new ones too. I really think this is an Alt problem, or regulator. I DO have a UDP on the car but, it looks as though Gordo DID replace the Alt pulley with a smaller one as this was my immediate thought. The car runs fine any other time and every other way. Just when I come to a stop in gear after warm up or after putting it IN gear that it does this. Can anyone confirm my suspicions or have an idea? I was wondering about the coil packs , but shouldn't there be other symptoms?

[1meanz]

i didnt read the whole post, but i read the part that says it drops when you go into gear, and i saw the part where you have a udp, with an automatic, watch the rpms. it takes power away from the car when it goes into gear. my car done the EXACT same thing. (when it was an auto) would go from 14.5 to 13.8 (roughly) and the udp will make a difference. could be the alt also, although its new. it could still be working poorly.

if that didnt help im sorry. but ill try and read it later if noone else helps you

[Juglenaut]

Either your idle is to low or your alt has a bad regulator. Replacing the alt pully for a smaller one should make it spin faster. A bad cell in the battery can cause this. One other possibility it someting may be drawing a decent amount of current or a short that is not fused lightly.

[SuzukiGhostRider]

Car idles dead at 750 rpm , which as far as I know is the correct idle for these cars. The idle DOES drop with the volt guage though, but isn't that to be expected as the car runs off the charging system the Alt provides? I.E., if the alt is weak or bad, the idle will drop.
What bothers me is the Alt and Battery tested out good at idle, under load and in gear.
Jugle, what did you mean "a short that's not fused lightly" ? Is that a typo or do I need a translator,lol.

[91LQ1Lumina]

I say start looking for a corroded power, or ground connection. I know I have to track one down about every six months, because of all the load from the 400W amp I have in the trunk.