Hello Everyone,

1991 420SEL, 114,000 miles

The car has recently developed a cold start problem.

Sitting overnight:

When the car has been sitting overnight, it takes a good 5 seconds of cranking to get it started. Cranking speed is normal, but seems to be not getting enough fuel. When it does finally start, it runs smooth for 1/2 a second then stumbles/misses roughly 10 seconds before it suddenly smoothens out. During this period, light black smokes exits the tail pipe.


Sitting a few hours:

If the car has been sitting a few hours, it starts within 1 or 2 seconds of cranking with a slight stumble for a second then runs smooth. No smoke out the tail pipe.


Immediate restart:

The car fires right up if re-started right away. No smoke, no stumble.


The car has a lot of power; no driveability problems. Even under full throttle there is no smoke out the tailpipe. At around 100,000 miles the ignition cap and rotor were replaced for maintenance. It didn't exhibit any problems then. Upon searching the archive, I've found references to a leaky cold start valve that might be flooding the engine overnight causing hard starts. I also found references to temp sensors that control the cold start valve. Other than this problem, the car runs magnificently.

I'm armed with a digital Fluke VOM. I'd like to know if there is anything I can test with it and how. My inclination is a leaky cold start valve (or other injector) causing some flooding; hence the light black smoke after sitting overnight. I've thought about the cold start valve not functioning at all and therefore not richening the mxture for a cold start. I was thinking maybe I could depress the air flow meter plate slightly (I think this will richen the mixture) during cold startup to see if it helps.

I would appreciate any help, thanks in advance

Nolan