My MB mechanic cannot figure out what could be causing the rough idle on my 560SL. Here's what we know it is NOT:

Vacuum leak
Fuel injector nozzles
Engine compression
Fuel filter
Spark plugs
Wires
Distributer cap/roter
Fuel distributer

I've purchased new plugs, wires, distributer cap, and roter, new fuel distributer, and had the compression tested. The new stuff did help some, but you still smell gas when it idles.

HELP!

A gas engine needs 3 things to work: fuel, air and spark.
Electrical problems are the most common, and most difficult to track down. The smell of gas indicates unburned fuel.

Has your mech. used a scope or diagnostic analyzer to check the firing pulse waveforms (shapes) and timing for every spark plug?
How is the signal on the crankshaft position sensor to the ECU? If that is erratic, then the entire ignition timing is messed up.
I'm not familiar with the 560 SL, but does it have a centrifugal advance on the distributor to adjust the timing? It might be failing to return to its idle position.

The other problem could be with the fuel system. Has the pressure been checked? You say the FI nozzles are not a problem - were they checked for on/off operation and spray pattern? It's possible one or more FI is not shuttng off, thereby giving much more gas at idle than needed. You need to check the wires and electrical signals of the injectors to make sure all are shutting off appropriately.

Good luck

I would check the gas lines, the fuel pump (probably in the gas tank), and the choke.