I just replaced the plugs myself, with Super Copper Bosch, no problem on initial start up, no problem once moving, what should I check for?

Do you think it might be carbon build up on the pistons?

The spark plug connectors had light oxidation/rust on them but seemed fine. Should I replace?

Thank you very much for any suggestions offered.
Mike McKinney

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1989 300CE - 269,000 km
1994 SL600 - 59,000 km