My 400e starts well when cold, then it requires some extra cranks when warm. This started after a tune up. Does this sound like a crank angle sensor?
Starting on 1992 Mercedes-Benz 400E
I had a similar issue. My 92 400e also ran rough when normal operating temp was reached. Tried changing plugs, air filters. Ran better cold but no change to the rough start and run at normal operating temp. I found a 4 year old post somewhere that discussed a temp sensor that tells the computer engine temp so the system can adjust the fuel/air mix accordingly. If bad, will not have an effect when engine is cold since the 'bad' output is what the computer needs to see for cold operation. However, when the temp goes up, the output should change but does not when it is bad. In my case, it wasn't bad but the connection point seems to have had some surface deposits that insulated the connection. After I checked it (it checked out as good), I was sad, but once I put the connector back on, it cleared the issue. To access, remove the black plastic cover that snaps on to the big air filter housing. It has vent slots cut into it. It snaps on to two posts on the air filter housing. Pull straight up from each side. You will see a couple of sensors coming from the engine. One has a single wire with a round connector (to the left) and the other has a larger connector with two wires (to the right). That's the one you want. Pull off the connector (have to press lock tabs). You may break one because they get brittle because of the heat, but not to worry as the connection is really tight. If you have a multi meter, check the resistance across the two post on the sensor. It should be different between cold and normal operation temp. Not sure what it is but if it's bad, it will likely not change. You can probably find some data on the correct resistance levels it you think you need them. Hope this helps