I have a 1988 560SL. It starts right up when cold, but when warmed up, it starts hard. It also has a low speed miss, but runs good at speeds above 30 MPH. I changed plugs. I hate to just start changing things when a distributor cap is $150+ and a rotor is another $40.

 

check your spark plug wires for any cracks or arcing when engine idles. they're not cheap but if you have over 100,000 miles on it it's possible that you need a new one. also check your fuel pressure return valve at the fuel pump. it may be leaking causing hard startr when engine is warm.