what kind of plugs are you using? Are they the right 'temp'? Were they gapped properly?
If that's all ok, check the timing. Check your Throttle Position Sensors. They might be corroded and be in need of cleaning. Make sure you don't have any vacuum leaks, so check your hoses.
If your car is a 90, like I'm assuming, the ECU is an OBDI not an OBDII. Therefore, running a diagnostic is an easy DIY procedure. Because of the age of the car you can't take it to a shop to have them hook it up to a machine. That only works on vehicles that were made in '95 and after. Go here to learn the diagnostic procedure.
http://www.ttzd.com/tech/diagnostictech.html