It could be from sitting, but also from age and mileage. Your injectors may be getting weak and losing pressure, your accumulator the same.

Your idle speed is where you should be with a cold engine. Could be the idle relay, or the temp sensor at the back of the engine.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe