I second the tank removal & clean..........or at least R & R the in-tank screen and check for crud (as a MB Diesel owner you probably have alot of experience with this operation!)...........on my w123 you can also look down the sender hole with a torch to get an idea of the crud in the tank (not sure about the 190E)

Really I strongly suggest you 'Bite the Bullet' and pull the tank……start at the top and work down stream to clear all the supply system

I learnt the hard way when I got my 1978 280CE going again after sitting for 5yrs ...........PSFRED's advice....."Dump the injector cleaner into the tank, jumper the fuel pump relay, and let the pump run for an hour or so -- this will clean all the varnish out of the fuel distributor".........was a very effective way of cleaning out my FD full of 'peanut butter'.......but I later had trouble with stalling after 15mins running which was traced to clogging up of the in-tank screen.......cost me a replacement fuel pump and quite a bit of diagnostic time (sounds like the fuel pump on the 190E is already ceased with varnish----injector cleaner & a few hits with a dead blow hammer with 12V applied sometimes clears them)

I first used an injector cleaner at ~130 times the usual dose (full bottle in tank with only a gallon or two) to circulate as PSFRED suggested and later carefully pressed the air flow plate until I could feel the vibration of fuel flow to each of the injectors

Hopefully the 190E won't be as bad as my 280CE .....but I wish I had started with pulling and cleaning the tank..........not as difficult as I expected (on a w123 anyway)