53 c class 200 compressor, 104k miles

I have owned this vehicle for almost 4 years, I noticed the temp gauge on really cold days hardly moved off the end stop. At the next service the thermostat was replaced and a healthy 85c registers.
However everytime I am stuck in traffic the engine management light comes on, but no error shows, even at the service garage no error?
I was advised it would clear in 3 days, and it does,
However on warm starts a very slight missfire is evident and on two occations it was so bad the vehicle would not drive. Switched off the ignition, re started, no problem drives fine.
At the last service the mass airflow sensor was replaced, but the problem still persists.
Ideas anyone??