1991 Plymouth Laser

Engine Performance problem
1991 Plymouth Laser 4 cyl Two Wheel Drive Automatic
2.0 Non-turbo

I went to get into my vehicle to go to work one morning and the car started sputtering, and lacks power and it shutters when you are stopped at a light. It actually bounces up and down while in your seat. Just replaced my oxygen sensor, fuel filter, performance down pipe, air filter and spark plugs. Check engine light comes on now. Its got poor exceleration, it sounds like the motor is bogging down. No oil in coolant. Installed K& N performance air filter. Problems started before replaced the performane down pipe. When it started the exhaust sounded real loud. So then I replaced the down pipe, no change in performance. RPM's at 750 in park, 500 in drive.
What could the problem be?
February 13, 2009.

Hi: If the check engine light is on, have the computer scanned for codes. Most nationally recognized parts stores will do it for free.

Let me know what you find.