I have an '87 190E that had very similiar problems. Ran very poorly, no power, idled like it would stall, low power, slam-shifted every gear!
I changed the plugs, cap and wires. I bled the injection lines at the fuel distributor (be careful of raw fuel spilling over a hot engine) and then I did my favorite:
The super tonic remedy: Add two bottles of Techron Injector Cleaner, ideally on less than a full tank, and drive it. Drive it hot and hard.
It could be your injectors are just plain dirty. Start with this and see how it goes.
A link about this: