89 Tbird stalls when in gear

Out of the blue, my T-bird stalls or just about stalls when I put it in gear. If it manages to run while in gear I have to ease into acceleration otherwise it starts stalling.

I've taken it into a mechanic and after 5 days, he says he has no idea what is wrong with it.

Fuel pump, pressure, filter are fine, replaced every sensor he could think of. Not a timing thing, chain, gears, etc.

I'm not very mechanically enclined so the fact that he said he couldn't figure it out is making me nervous.

Any help or ideas would be appreciated.

you are looking for a BAD vacuum leak