Do a search for OVP to locate it for this car (check through the 'FastLane' catalog for a picture of it), then pull it out and check driveability. This car uses Bosch KE engine management, which has electronic fine-tuning of a basically mechanical system. The OVP is a relay which provides power to the ECU, so pulling the relay disables any electronic control - reverting to mechanical injection.
Now, if the engine continues to have poor driveability with the OVP removed, then ignition or mechanical injection components are suspect and need replacing. This would include vacuum connections and air supply hoses in the idle system, coil, plugs, wires, etc. If it runs pretty well - and much better than before, then the ECU is screwing up operation, probably due to a failed input sensor or bad contacts in the OVP you removed.
Note with the OVP removed, emissions will be out-of-whack and ABS disabled, so consider this as a diagnostic, not a solution.