Hello all, I think this site is great. I sent many hours reading the posts before I bought my first Benz. My 91 190E 2.3 with 160k has a bit of an idle issue. About one week ago when I put the car in park the idle started climbing, it topped out at about 2500 RPM's. I restarted the car and all was well. Then today I was driving was cruising at about 75 gunned it to about 95 then went back to 75ish. When I can to a stop light a later the idle was very erratic, dipping down to 500 rpm then surging up. It felt as if the car was going to stall but never did. Then tonight I started the car to pull it in the garage, it would not stay running. I finely got it in the garage.
So does anyone have any advise on where to start looking tomorrow? All input is welcome. Thanks

Absent of any rudimentary diagnostics I would look at the OVP relay.

If that is ok I would then buy the $30 multimeter from sears (make sure it has a duty cycle % reading) and read some more post because you've pretty much covered all the bad idling scenarios in your post and the cause could be anything.