Starting getting more difficult...seems fuel starved?

[glenmore]

I've had my 1991 300CE, 138m for almost 4 years now. The start has never been perfect, always a pause, a stumble and then the engine finally catching. Once in awhile after a cool evening I would get an instant first start in the morning with the engine revving higher to warm up the car. This must be the cold start valve working correctly? Hot starts ( after 5 minutes or so) are also good instant starts. But the rest of the time it is pause, stumble and finally catching. Recently now the pause is even longer before the engine finally catches. If it doesn't start and then I immediately try again, then it starts a little quicker with the same stumble. It seems fuel starved on start up. Otherwise the car runs and idles perfectly.

Where should I start and what items should I check?

Thanks,

glenmore
1991 300CE
2000 C280
1990 LS400