I agree with saumil, you may have a clogged ‘cat’. I had one on my SL600 and the symptoms were similar to yours, but not drastic as my SL has a pair of catalytic convertors; one for each bank of cylinders. In my case, the car would drive but was very unresponsive. Idle was rough (but tolerable), however getting my SL up to highway speeds quickly overheated the engine.

When the offending ‘cat’ was removed from my car, a ton of fine powder/sand came out of the exhaust end of the ‘cat’. The honeycomb inside the ‘cat’ had somehow become loose and driving vibration caused it to abrade itself inside the ‘cat’. The powder/sand eventually built up enough to block the engine exhaust.

In your case, the problem may have been steadily getting worse and when you changed the Oxygen Sensor, coincidentally, the ‘cat’ may have finally plugged up good to its current state.

Just a thought, but worth investigating.

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'96 SL600 (105K) Triple Black - Mein über-Fräulein
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