Starter won't disengage 300E
 

Lately I've had a weird issue with the starter. I'm getting a grinding noise when I release the key upon starting and worse yet a couple of times the car started and the starter wouldn't disengage. I turned off the ignition and the car was still running and the starter still engaged! I could even pull out the key. Only when I turned the key to 'start' and then 'off' could I stop it.

Should I be looking at cleaning the ignition switch contacts or the starter motor itself?

Correction: when I removed the key I don't think the car was still running maybe just the starter motor was still turning over the engine very fast. Starter solenoid bad?

As far as I know there is a king of clutch on the strater motor activated by the solenoid.

that part is sometimes dirty.

lets us know

I encountered that problem with my 240D (halfway through a transcontinental trip) in January. I pulled the shutoff line and only started it once a day and just left it running until I got to my destination, where I was able to replace the starter. That fixed it.

it sounds to me like its a faulty ignition switch,remember the starter solenoid is only powered up when the key is in the start position,i can understand that a sticking solenoid could cause this issue,but the solenoid cant stick if its not getting power from the ignition switch,you may have bad contacts in your ignition switch,try spraying in some graphite into the key slot run the key in and out,wiggle it back and forth ,see if this helps.but id lean towards the ignition not the starter,just my opinion,goodluck.

I sprayed the inside of the ignition switch but I will probably have to take it out to get to the contacts. Looks a bit easier than pulling the starter.