David, you are thinking exactly like I am thinking. Actually I replaced the connectors and wires for my friend (from whom I purchased the car) when he began getting misfire codes just last August. Replacing these along with the plugs resolved that issue. Actually, at the time the codes were being triggered, the car was running fine and you couldn't even "feel" a misfire.

I have been thinking about the MAF, but wouldn't that throw a code as well? Is MAF cleaner actually useful?

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280