I am having the same problem as you.
Bad mpg (from 420km per tank to 260km) and smokin'!
Problem consistent cold/hot, eha on/off.
Can get a smooth idle but smoking really bad.
If I lean the mixture, smokin' less but idle really crappy (of course).
Also, while checking the fuel pressure regulator (read in a post somewhere that if it leaks fuel it's history), pulled off "vac" hose and broke it!
There is fuel leaking from the regulator anyway and I will replace the "vac" line and breather hoses as they're crappy anyway.
You changed your regulator and it didn't help at all?
I was also looking to do this but it's a 200 dollar part so I want to do some tests before I swap it out.
I have access to my kid brother's 190e (identical year/model) which is currently in good running condition (powerful at 21% duty cycle but lower mpg - 380km per tank) and will swap the part to see if it makes a difference (I doubt it).
I have recently posted my problem and I'm also closely following yours.
I was recently recommended to another Merc techie and hope this guy (he'll be the 3rd) can sort this out for me.Else, I'm on my own!
Best of luck, and I'll inform you as soon as there is a breakthru'.