I'm with post #4. The first year of the W210 did not have a TPS(the USA cars came that way). It did not have Drive By Wire system. The transmission was all hydraulic, and the throttle cable goes straight to the throttle body lever.

I would investigate your intake for something plugged, and the throttle butterfly can have the edges plugged with black blowby goup, and/or the little bypass hole is plugged.

I would remove the top of the intake over the engine, and clean down the throttle butterfly lever with a cloth and carburetor cleaner.

Smell the fuel regulator. it should not smell like fuel. How is the fuel filter?

Maybe you have a crack on the intake manifold. i would spray engine starter fluid on a cold engine around the intake manifold to see if the engine changes speed.

Martin