W126 (1990) ignition problems

[jhastie]

I have a 1990 MB 420SEL. It starts easily but stumbles and backfires when it is cold. As soon as my Temp guage needle reaches the first tick mark it smoothes out and runs well.

I recently replaced the distributor cap and rotor, the fuel pump relay (pump works) and plugs. I used a timing light and noticed that the spark was not occuring steadily. I ordered a new coil. The engine is now running rougher and it quits when I stop.

Is there any way to test the Ignition Control Module (Bosch 0 227 400 693)?