The cat converter most likely needs replacing. The engine is not getting the exhaust out and it's producing overpressure in the engine. Don't drive it for long like this your turbocharger won't survive it. This can also be caused by a clogged airfilter.

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600SEL '91
300E 4Matic '88
240D '83
280SE '77
350SE '73
The most complex systems can fail in the simplest way.
Contra verbosus noli contendere verbis, sermo datur cunctis, animi sapientia paucis.

i don't believe in the lord! He's never bought me a Mercedes Benz.