1988 300SE Warm Start Problem
 

I have replaced the injector regulator and injection pump relay. I have no problem with cold starts or hot starts, but after about 30 min., it is hard to start and works best by opening the throtle control or putting the pedal down and giving it air. The car runs fine otherwise. Seems to be gas accumulates in the intake after turning it off. The car has 42,367 miles-very low. Have put a can of BG 44 in the gas.

What parts would cause this? How do you trouble shoot this?

The accumulator perhaps, does it start easy hot after, say, 15 minutes?

Try New Injectors
 

Much has been written on this subject.

Classic symptom for a M103 engine.

The owner's manual suggests use of throttle for warm engine start!

Seems that new injectors is the likely best fix so long as all other fuel system components are well serviced.

100k miles seems the general consensus for the life of these items.

89 300CE

155k kms.

Ha!!
Had the same problem a few weeks ago.
Drove on a trip and put in a can of Fuel injector cleaner.....3 days later the EHA valve started leaking gas, so I had to replace it. Now it starts up fine hot or cold.
I did notice that my gas gauge is acting funny now, hopefully the STP crap I put in the tank didnt do more harm than good.