rough idle in drive

[JNROX24]

ok guys here we go i have a 90 beretta with 3.1 the problem i have is the motor runs great when in park but when put in drive starts to run rough and has a hesatation when taking off replaced plugs, wires, air filter and cleaned intake. i know the coil packs go bad but y only in drive does it do it could it be something else?

[Schrade]

Wow! How come you replaced all that stuff? Was it bad?

Maybe do a fuel pressure test (see youtube 'fuel pressure test'). Any loping at idle? Check for vacuum leaks.

Loping idle is vacuum leak. 30 year old lawnmower, or a new car on the lot. If it sucks air where it ain't supposed to, it lopes.

Brick on pedal, block TB arm, anything to get a STEADY idle. 1200rpms or so... Feed starting fluid spray, A LITTLE AT A TIME, EVERYWHERE. Rev increase is the leak.

In a tough spot to pinpoint? Light a book of matches, blow it out while the heads are burnin', and feed the smoke to the leak.