I had a problem with my E320 stalling and sometimes it wouldn't start if warm. It ended up being the knock sensor. I saw no DTCs with a simple scanner, but my mechanic caught it with his scanner after several visits. He also contacted a MB factory rep. about the problem. The MB rep. said that they are seeing more knock sensors fail on the older w210s.

I was only charged 1hr labor for diagnosis and replacement, so I imagine it isn't too hard to replace. I never found out where it was located though.

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1998 E320 120K mi
1991 Miata 80K mi
2001 Ranger 109K mi