On the 190E 2.3 it had a horrible idle and didn't pull very well (low power) when we first looked at it. Did a bunch of stuff: cap, rotor, plugs, wires etc.
But then a tech friend suggested cracking the fuel distrib lines at the fuel distrib. A bunch of brown nasty came out. I then did it at the injectors. Same.
Then did the "double-dose of Techron" injector cleaner in less than a half tank of fuel. Still bad for a few minutes. Let it get warm, revved it up and down a bit and then a pronounced "thwump" and now runs like a champ.
Not a universal cure all but I thought I'd pass it along.
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)