420 SEL cold start problem
 

Hi I have a 1989 420 SEL with 340,000 miles on it. When it is cold outside, and the engine is warm it starts and purrs like a kitten. If the car sits out overnight and the temp is below 30 degrees the car starts very hard. It turns over very well, but doesn't want to fire until it has cranked about 30 seconds. Then it fires on one or two cylinders for a little bit then finally starts and runs fine. Any suggestions? Wet or dry weather doesn't seem to affect the car. Has a new battery that is the proper size and CCAs.
Thanks
Don

My only theory would be the temperature causing your issue. Since it is that cold, your oil is a thicker hence your motor working alittle harder when very cold. My car has somewhat experienced your issue in the past and what I do is just crank the motor 1-2 seconds a little longer and my car doesnt do the problem as much

Sponge Bob
 

We have seen many engines with cold start problems that can be attributed to carbonized intake valve faces. The heavy carbon deposits absorb the atomized fuel from the nozzle like a sponge. You may try adjusting the fuel mixture slightly in the rich direction but that would only be a Band-Aid.
Peace