If it's idling rough, one of the two oxygen sensors could be out. You may be able to detect by checking the error readout. Remove the kick panel, passenger side. Behind you'll find a two pin female coupling (yellow?). Insert a wire, effectively completing the circuit. Turn on your ignition, first or second position if memory serves (don't start the engine).

One of the lights in your instrument cluster will begin blinking (can't recall which one but it will be obvious). Unfortunately, you need to have the codes. I will look them up if I still have them. You may do a web search to find them.

I used this method to verify that my speedometer cable was out as well as a possible O2 sensor on my '92 LS.

Best of luck.