95 C280,new plugs, good wires, OVP ok, still runs horrible

I am stumped now, I'v eput new plugs in the car, I didn't replace the ignition wires but they look good and I see no sparks when sprayed with a fine mist of water at night, the OVP sensor is the upgraded part #.
And the car is running progressivley worse. It used to run ok if you restarted the engine. now that only seem so work for a minute or so.
How do I go about retrieving the trouble codes for the car. Or is there other parts that should be replaced?
Any advice on what could be making the car run so bad? Please!

Thanks
Shawn