It could be that using a fuel system cleaner is different than an injector cleaner.
I don't think you need to add fuel system cleaner with every tankful. I don't.
What brand of fuel do you use?
Which plugs (Beru) are you using?
What do you do with your foot when it starts?
Have you tried turning on the key and then waiting two seconds?
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)