Thanks for the input guys. Mine is the 12 valve M103 engine, sorry I didn't mention that. Plugs have been changed recently and the rotor was changed a few years ago. Not sure about the HT leads and distributor cap, will have to check my receipts. I'll also look into the temperature sensors.

In terms of the ignition system is there much evidence of issues with the ignition coil?

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Want: CL500, 1997, has to be black!

1990 300CE
Black exterior, Cream Leather, 149k
1988 300E
Gold exterior, Beige cloth, unknown miles , sold
1998 S500L
Black exterior, Cream Leather, 41k, sold