TDImne

hello every one,i firist want to apologise for my bad english,and i have a few questions regarding my 1999 a6 2.5 tdi afb engine code.
my abs ecy doesn't work. and since it got broke my gear changes went "funny" .while driving on 2000 rpm it changes gear down,then up,all the time wthout touching the gear or throtle. i took it to a workshop,and they say it's because of faulty abs ecu. could it be?
and also, it goes sudenly into limp mode while driving it normal.
second problem is what i think is the MAF sensor. first start of the engine in the morning,it goes into limp mode?
before a few day i started overtaking a car, hit the kickdown, it went to 3500 rpm then it staled,and boom again limp mode.
could anyone please tell me if they had any similar expirience with their tdi engines and what do you think of the problems?
thank you...