What the mechanic did....
The total bill for diagnosing and fixing the problem came out to 4 hours X $60/hour. He ran a complete test on both the electrical and mechanical sides of the fuel distribution system. Then he did a leak down test on both banks. Then he adjusted the #6 exhaust valve and replaced the rocker shims (two little metal shims). The shims were $7.50 for the two shims. This was far, far less than what the dealer charged me t replace parts that didn't fix the problem. I also had him replace the spark plug wires. For a fraction of the cost, my car runs so smooth it is incredible. M-Bs will never run as smooth as Lexus, but the previous roughness in mine was unacceptable.
I hope this helps. I hope your mechanic can diagnose and fix your problem. My mechanic told me that a tight or sitcky exhaust valve tends to overheat and will eventually fail.
1989 300TE "Alice"
1990 300CE "Sam Spade"
1991 300CE "Beowulf" RIP (06.1991 - 10.10.2007)
1998 E320 "Orson"
2002 C320 Wagon "Molly Fox"
Res non semper sunt quae esse videntur
Not in this weather!