I do not think that it's adjustable. I would make sure that the petal goes perfectly into the slot @ the kickdown switch. Maybe the switch just needs to be pulled up or something?!
Before my kickdown switch permanently stopped working, it was not doing a prominent click as it should. So your switch still MAY be the culprit. I'd first see if you can align them to make sure they are lining up properly.

Also, maybe your throttle linkage needs to be lubed?

GOod luck...

__________________
2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)