500 sel cold start idle - rough idle on cold start

[DENNIS]

My 87 500SEL has developed a cold start problem since the drop in temperatures recently. It is slow to start with normal cranking speed but when it starts it has a very uneven idle with the speed going up and down. The economy gauge also moves around whilst cold idling. Also it cuts out when trying to accelerate.
It seems that it is runing very rich at this point as it produces a lot of black smoke.
HELP.

 

[Gary]

500 sel cold start idle

As I know, the cold start valve will only be operate in a short period, during you start the engine, so, I think the uneven idle problem is not causing by the cold start valve. I know a method of testing the cold start valve, you can simnply disconnect the wiring connector, and tyr to start in cold and see whether it have any different, if it can't start or exteremely difficult to start, than this mean your cold start valve is working.

If it cut out when you trying to accelerate, than is poeeiblly too rich, as to much fuel kill the spark. or your igintion system have problem. Try to get the spark plug out and see what it look.

For the rich running problem, you can try the emission test and see whether is too rich or not.