I had a similar problem with my '86 some years ago. Wouldn't idle, MAS code etc, always stalled at the lights and made me look an incompetent driver unable to keep the car going, or the other extreme being a dickhead always revving the car at the lights.
A number of supposed experts also agreed that the MAS would be the likely problem. Another "expert" told me that the fuel injection system was stuffed and that I should replace it with a Motec system, (he was a Motec supplier - possible conflict of interest?)
After buying a brand new MAS at $600, that did not fix the problem either.
Guess what. There is a solenoid (Fuel Vapor Canister Solenoid) which should be located just near the canister in the front left well of the engine bay.
I replaced the solenoid with a second hand $5 one from an '85 (coincidence) and the problem was largely solved. Then I discovered that the rubber hose ends were a little frayed, trimmed of an inch or so and improved the seal, and things were better yet.
Whilst you're at it, you might as well check that all your vacuum lines for leakage They're cheap to replace anyway, just be careful to make sure that you get the exact right size - from my experience little things can make such a big difference.
So now I still have a brand new, still-in-the-box MAS, a $600 conversation peice.
