if its running fine on the highway and acts up only at idle, tham I would say while the car is at idle remove airclaener and with a flashlight in hand look down inside the tbi and see what the spray pattern comming from the injector looks like, it should by very fine fuel mist and no dripping . if not get a good fuel system cleaner and let it run through for a while and then replace the fuel filter.

on these cars a little water in the gas can cause the same problems, so look for that as well.