I had the car (91 305 tbi automatic) in the shop for something else and the guy said my car isn't firing on all cylinders in gear. it seemed odd to me that it was firing on all cylinders in park but not in gear but I'm almost certain that's what the guy said. it does have a shaky idle in gear. I haven't looked for anything on this issue yet. I thought I would ask you guys where I should start or if you have had or seen a similar issue.

 

Start with a tuneup. Cap , rotor , plugs and wires.
If that doesn't fix it do a compression test.