Good Morning, I pulled all plugs and found one of them looked new while the other five showed firing? Is it the coil? I have a E200TXECM 1998. I can get on plane but cant reach top end.
A clean new-looking spark plug can be the indicator of water infiltration. Perorm a compression test and put a timing light on each spark plug wire. Report back on your findings.
Hopefully head gasket. Cheap and easy repair. If it is the head gasket then make sure your cooling system is doing it's job correctly. Could have warped a little due to overheat. Make sure mating surfaces are nice and flat before fitting new gasket.
