c280 engine running rough
 

i have a 1994 c280. On a trip it started to miss about 100 miles after a fillup. When cold it runs fine until warm. Even when warm sometimes it runs ok after being off for 10 min. Seems to be getting worse, but still smooth when cold. Changed the fuel filter and plugs. Old plugs all looked normal. All cyls 150 psi warm. Car has 120,000 mi

recently replaced the OVP relay.

Has the engine harness ever been replaced? Any fault codes being stored?

the harness is original. The wiring on the top of the engine to the injectors appears to not be brittle. I plan to have the codes run. Thx