I've got an '88 Trans Am with the LO3. Sometimes when my car idles, the tach shows the RPM's bounce up and down. I just replaced the rotor, and it didn't fix it. I had the cap and wires replaced when I had a tune-up...about a year ago. Does anyone know what could be the possible cause?

 

maybe it could be your disty gear being bad to make it jump.

 

Sometimes this happens when your alternator is going out.

 

I have noticed that once or twice, after this started happening, that my lights dim a lot, and my volt guage goes down to the red for a split second, then come back to normal. Also, when it's idling, the volt guage ticks back and forth just a hair....I didn't think that was normal. The only thing is that I had the battery and alternator replaced about 6 months ago too. The alternator was a rebuilt unit tho. They've got warranties tho.
What do you think about these conditions?

 

well I do have to agree that it does sounds like you have a voltage problem. Since you said that it has a new battery and alternator, you might wanna check your main ground going to the engine and also the main positive going to the starter. You might have a bad cable somewhere so do a volt drop test and maybe a resistance test too.

 

Well, I'll take it to Firestone and have the charging system checked. I'm just curious why would the alternator going out, have an effect on the tachometer. I just don't understand. Thanks

 

tachometer is the most sensitive guage in your car when it comes to voltage spikes. You'll see spikes on the tach long before you'd see spikes on your voltmeter.

 

I think I might have found the problem. The wire from my alternator has a fusible link at the end of it (rubber that burns up so that it protects the circuit). The alternator wire connects to a make-shift sort-of junction box of other wires. And then a smaller wire connects it to the battery. I think the small wires can't carry the current to the battery, thus causing a voltage spike. Do ya'll think this might be the problem? I've attached my crappy drawing of what I'm talking about. My digital camera took a crap the other day, so I can't get a pic.

 

Forgot the pic...whoops.

 

MAKE SURE ALL YOUR PLUG WIRES ARE CONNECTED!!

One of mine came a little loose (boot still hanging on the plug) in the summer and it did that.

Might be different though, mines a '83 4bbl, but its an easy thing to check.

 

Yeah, that happened to me once too. I'm pretty sure all the plugs and wires are ok...but I'm gonna double check this weekend. Also, does anyone know if what my pic describes is the way the car came? Or is it something the other owner did? Could someone post a pic of their wires from the alt. to the battery on an LO3? Thanks,

 

Hmm my rpm gauge is doing that to when i am driving also i feel a loss of power when it is fluctuating. I thought it was somthing to do with the fuel system but while stopping at the ATM the other night my wife said it looked like the lights went dim a little. I may have the same problem as you do.


Just check my battery and the corrosion I cleaned off the connectors is back and some of it is on the wires. Im not sure if this is causing it though because this corrosion has a orange taste to it unlike the harmful corrosion that tastes like melted plastic.

 

I hooked up the Tech 1 today and it said I had a Code 23. Low inlet air temp...or something like that. Would this cause another problem in the car's driveability? Also, my tranny is shiftinga LOT sooner than normal now. It usually shifted to 2nd at around 3 grand....now it does it at 2. Could it be a valve body in the tranny?...I just had the tranny rebuilt 6 months ago. Sorry for all the questions.......I just though maybe someone could help me. Thanks,
---Matt---