Remember the ECU will kill the fuel injector on a cylinder with dead miss. This will be in memory as code..... being as P0300 is Random Miss Fire I'd look for,
vac' leaks are most common as are wiring harness concerns....try the 'wriggle test' on the wire harness.

Fuel pressure ?

Have you a Mercedes compatible scanner? If so check engine smoothness.

Are you running 100% pure 91 super gasoline ? Any possibility of water in tank?



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