You can first read the codes from your on board diagnostic unit (OBD) and they might tell you for example "injector problem" so you can clean those connectors. Or you can clear the codes and see what developes again. A Bentley manual would be best but if you don't want one, we can send you the method. As I recall, you take the cover off the OBD little black box, on the drivers side of the engine compartment and put the pin in position 2 (?). If you want to do it, I can check the protocol for sure. Then for about 1 second you push the button. The ignition is ON but the car is not running at this time. Then watch the blink pattern. {2 (rapid) ........ 2 (rapid) ...... 1 ................} means something specific is detected and one set of blinks might be followed by another set. Write them down and read the chart. It is pretty slow so you have to wait them all out. 5-10 seconds between groups. Then you know where to begin. How does thecar run? I would not worry too much if it runs fine.
If worse comes to worse and you need an ECU (fuel injection brain) or air mass meter, do not panic and buy retail! The 89-on cars have the sometimes frail 561/591 ECU and the mortal 016 air meter. Neither needs to be a big expense and you should be able to get good used ones from someone on the board. Always check the board, and always doubt your mechanics diagnosis. 75% of the time we can fix it for a song, if you want to work a little bit.