So just bought a 1998 SL500 with 115k miles. Car can not go over 3000 rpm and has no power. The car would idle fine and be fine up to 2000 rpm can go higher than that up to 3000rpm but it will overheat. Now it does this in P, N or driving. When driving has almost no power. I did the spark plugs. It has M119 engine and the little plastic tubes by the cam that take oil to the lifter, three of them where broken so I replaced them. I haven't lost any water. The level hasn't changed. And I don't see water in oil. But I do see some smoke coming out of the oil dipstick and oil filler cap.

Also car does not blow cold (not even outside air) even when Climate control put to cold(A/C) in the interior. In the cabin it will always blow hot air. Not sure if these are related.

My guess is that I might have a badly clogged catalyc converter. This is what I did to test it since I could not remove any O2 sensors. I took out one of the spark plugs and run the engine for a few seconds. With one spark plug out the car would rev up to 4200 rpm.
So I am thinking my catalyc converter or muffler may be clogged really bad.
The check engine light is on and has cyl 2 and cyl 4 misfire code but the plugs are new from Mercedes Benz and I have switched the coils around to make sure it is not the coils. Still getting the spark plugs misfire code.

Now I do all this more as a hobby and I am not a mechanic so I wanted to ask for an experienced advice what you think? Have you seen this before?

Thank you and sorry for my English.

I only paid US $4000. Can't return it. I knew I was gambling.