I have a 87 Trans Am with a LG4 engine. The car starts fine but when I put the car in drive or reverse the RPMs go up and down for a few seconds and the car stalls out. Even after the car warms up the car still stalls when in drive or reverse. I had the carb rebuilt, the problem went away for a couple week and the it came back. Can anyone help me

 

If you have a cat, check to make sure it isn't clogged.
Change your fuel filter.

 

make sure you don't have any vacuum leaks, try spraying some carb cleaner where any gaskets are and if the RPMs go up you'll need to reseal those areas

 

Is the Idle set right? How long since a tune up? Fuel filter is probably the first thing to check. I dont think a vacuum leak is the problem, that would more than likely raise the Idle. But check anyways. I found the best way to check for vacuum leaks is with a torch, just not lit. The hand held propane torches, the ones plumbers use. You know.

 

cap and rotor ? I know you prabably checked your plug wires sence you messed with the carb . Goodluck man !