I would steer clear of the guy with the valve guide story. Injectors possible I suppose, but as mentioned already, I'd be suspicious of loose/leaking vacuum hoses, idle control valve, throttle position sensor.

Over the years, there have been countless writeups here about these sort of problems with 300Es and any car for that matter with the M103 motor.

I would query the SEARCH function. Long list of possiblilties.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"