I bought a 1991 trans am with a 350tpi. When i bought the car it was sitting for six years witha bad fuel pump. I replaced the fuel pump fuel filter sending unit and cleaned out the tank. Changed the spark plugs the wires the cap coil and the map sensor and of course changed the oil. The problem is it runs great in park with no misses or anything even when reving the engine but as soon as i put it in drive it gets a real bad miss what can be the cause of the miss in drive and not and park? Im so lost

 

Did you check fuel injectors? I would OHM test them.

 

No load on the engine out of gear so little spark needed to keep it running
You appear to have a weak spark that won't support the engine under load ;
just because you can " see" a spark with the plug out , doesn't mean it is strong enough
to fire the wet plug when in the cylinder)

I would do a full check of the spark system

Ref
http://easyautodiagnostics.com/gm_ic...n_module_1.php

 

I cant believe after 6 years you don't need injectors. Mine sat for 2 and I just had to change the injectors. I got it running with the old ones, but not very well. With new Bosch III's purrs like a kitten.