Rob, why not take your 190 to a Mercedes Benz dealer?
You are being jacked around by mechanics that don't know where the problem is so they just cover every aspect, parts replacers.
Do yourself and your 190 a good turn and go to the Dealer.
Our moderator suggested the intake cam may have jumped a tooth or so;
I question the cat/convertor?
Happy Trails Beep Beep from Houston!!!
Donald, El Cheapo