One of the first things you should always check when you have a performance problem at idle or running speeds is the spark plugs! After all, they are creating power with their activity and if they are fouled or otherwise impaired or the wiring harness is faulty, you will inevitably get poor results.

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Ben Harrison Carter
1999 Mercedes ML320 87K
1992 Mercedes 300CE 89K
1995 Corvette 29K -- Sold Dec 09
1989 Mercedes 420SEL 99K -- (Sold 4/08)
1968 Mercedes 230S (106K) (Sold 9/06))
1976 Mercedes 450SEL 130K (Just sold - 06)
1961 Mercedes 220Sb (sold years ago)