Could also be the warm-up compensator, or it's power supply.

But if you have to push the gas to start it, I wonder if you are getting any air through the idle valve at start. Maybe the idle control unit is failing, and keeping the valve closed until the coolant sensor opens.

Next time you try a cold start, pull the connector off the coolant sensor - rear of right cylinder head, under the throttle linkage - and see if that makes a difference. That will simulate a warm engine for the idle control unit. The idle will be low but the engine should run.

Also try a cold start with the idle valve unplugged. If you get the same problem, that would eliminate the idle system as a problem. You should get an "idle" around 1100 RPM.

If that doesn't make a difference, try unplugging the frequency valve before a cold start. If that makes a difference, then the lambda system may have gone off the deep end and is trying to lean the mixture at start. The valve is on the intake manifold near the valve cover on the left side. On my SL, it has a yellow connector with two wires.

Good luck.

__________________
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