[silicon212]

Originally Posted by stucknok

Forgot to mention that the check engine light does come on on the highway.

OK, do a quick check on the trouble code. You can do this by shunting pins A and B on the ALDL connector on driver side, under the dash and to the left of the steering column. Jumper the two pins together (you can use a paper clip if you wish) and turn the key ON, but DO NOT START the engine. The malfunction indicator lamp (MIL or Service Eng. Soon) will flash a series of flashes and pauses. You will see a flash-pause-flash-flash at first - this deciphers as Code 12 - this will repeat 3 times. Code 12 means the system is working properly, but is not receiving reference pulses from the distributor (because the engine's off). Next, you will see, in sequences of 3, whatever diagnostic trouble codes (DTCs) are saved in memory, incrementing until there are no more at which point the system will flash a Code 12 before repeating.

Pay no attention to the clicking you will hear from under the hood - this is the M/C solenoid on the carburetor being driven by the computer (you normally don't hear it because the engine is louder).

My guess is you will either see a Code 34 (flash-flash-flash-pause-flash-flash-flash-flash) or a Code 45 (flash-flash-flash-flash-pause-flash-flash-flash-flash-flash), meaning MAP sensor or running rich air/fuel mix. A catalytic restriction can sometimes show up as a Code 34 MAP sensor on these cars, because a restricted exhaust system will seriously drop engine vacuum (you can test for this with a vacuum gauge - should read around 15 in/hg at idle, rev engine and it will drop during revving, but should return to ~15 in/hg). A Code 45 can be either a plugged air filter (you said you changed it though) or a maladjusted/malfunctioning electric choke. Make sure the wire is firmly attached.