Defintely do the double-Techron dose in a less-than-full tank of fuel. The richer the mixture the greater the cleaning, within reason.
Have you checked your cap and rotor?
My take is dirty fuel system/injectors. Another tip is to CAREFULLY bleed the injector lines at the fuel distributor. A tech recommended this for the 190E. I did it twice and bled all sorts of crap out. I was really amazed.
Someone recently with a 420SEL with one clogged injector did this with good results
Keep us posted,
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)