Take off your air cleaner element ( 4 10mm nuts) and have a look at your throttle body. If it is dirty around the top region with possible carbon deposits, then the intake plenum is almost certainly pretty dirty with oily sludge and carbon deposits from your positive crankcase ventilation hose. There is a cool tool that does an outstanding job of cleaning out your throttle body and intake plenum and is better than harsh intake cleaners which could possibly damage an idle speed sensor or air flow sensor. Check out http://www.intakesnake.com
You'll notice your idle will be smooth as silk afterwards.
(Have you replaced your spark plugs latetly??? cheap to do)
Good luck with your 190E brother!!!