Check the inexpensive things first. Vacuum leaks are the obvious culprit. There are two vacuum lines which run across the rear firewall, under the windshield wiper motor and battery. They feed two vacuum reservoirs hidden in the passenger fenderwell. These lines are known the develop leaks, especially if any battery acid has spilled. Anyone who knows this car can test them in five minutes with a hand vacuum pump.

I had a slightly clunky/harsh 3-4 shift in my '93 sedan for several years. Eventually the climate system started changing to defrost during acceleration, a sure sign of vacuum leaks. Replacing the rotted sections of these lines not only fixed the vent problem, the trans shifted smoother, and the idle improved. I'd check it out before dropping bux for a new trans.

- JimY