Need help sorting out an intermittent problem with my 1991 300SL.

On a cold start, the engine will start but the mixture appears to be too lean. The engine idles perfectly but will stumble unless I start out in first gear. This condition will remain until the engine is up to normal temp and will improve as the engine warms up. this happens 2 out of ten times. If the intial cold start is good then I have not trouble. I have never had the problem when the engine is at operating temp.

New injectors and fuel filter did not help.

Any suggestions?

Dan