Also may want to check for a faulty coil. Not sure if that is your issue, but we were told to check this and that and we checked everything, but nothing helped until someone told us to replace the coil up by driver front of the engine.

Sounds strange, but when we were having problems with my moms '88 300SEL, turned out it was indeed the coil that was going bad. It would be difficult to start at times and sometimes when it would start as soon as you pushed the pedal it would stall. New coil and its been fine ever since and that was about 2 years ago.