With too much fuel(rich) all you do is waste gas and maybe damage your catalytic convertors. Only if your engine was running lean could you have some damage. I would get a compression/leak down test at another repair facility and go from there before spending any more money.

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2006 E320 CDI
1998 S320
1987 190E 2.3-16

1990 300D 2.5 Turbo(sold)
1987 300SDL Turbo(sold)
1987 300TD Turbo(sold)
1987 190D 2.5 Turbo 5sp(sold)
1985 190E 2.3-16(sold)
1984 500SEC(sold)
1984 230TE(sold)
1978 240D(sold)-Miss it!
1972 280SE 4.5(sold)