I went through a period with my 91 300SL with stalling and poor idling and the chased all of the usual fuels system issues. The problem was solved with a new ignition coil. Used regular NGK plugs. I would also suggest new rotor and distributor cap. This engine seems to need a very good spark from a sound ignition system and should be checked before all of the fuel system stuff.

Hope this helps.

sldan