97 E420 Hard Starting

Hello folks, I need a little help:

I have a 97 E420 with 77,000 miles. A week ago I started to experience troubles starting. At first it would take 2-3 seconds of cranking to get the engine to fire up. The engine does turn over fine though, and it seems there is plenty of power to the starter. Once it was running the engine idles rough, to the point sometimes that it seems like it is going to die but it catches itself and continues running. The hard starting and rough idling occur regardless of whether this is the first start in the morning or after the engine has been operating for 30 minutes. Today it took about 5 seconds of cranking to start. I have tried leaving the igntion key to on for 10 seconds and then cranking to see if the fuel system needed to be charged. This didn't help. My car does run good on the road and shows no hesitation when accelerating, I just see these problems during starting and idling. I have pulled the air-filter housing and cover and looked for any loose electrical connections or vacuum lines. I haven't seen anything that appears out of the ordinary (at least out of the ordinary too me, I am a novice). Can someone point me in a direction at things to check out? Fuel filter, pump, plugs, electrical system... What should I look at first? Any suggestions for additional tests I can perform to help isolate the problems? The check engine light has not come on and I have not seen any other warning lights.

Thanks!

-Chris