My 1990 300e suddenly started running rough and missing.

I replaced the plugs etc but no help.

I started looking around and there is a wire with a rubber plug hanging down next to the starter which has a single connector in the center, It must have just come loose because the contact inside the plug is clean and bright.

The wire originates at the back of the valve cover on the driver side and comes out of the harness running along the intake going to the ECM behind the battery. what might this be and where do I need to look for a socket to plug it back into?

Any help will be greatly appreciated

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