i went through a lot of probs trying to find out what was wrong with my car. i have alfa 156 jtd sportswagon.2001. i changed 5 injectors. mass sensor and map sensor and crank sensor. my car got so bad i would be driving and it would just cut out. if it helps. mass sensor will only stop car reving properly it would not stop it starting.map sensor is easy remove and clean, dont really go wrong, my injectors were replaced because they were over fueling car.i found my starting and cutting out problem. it was the dvr sensor on back of fuel pump.
my faults and many others on here and ive read plenty of forums all probly stem from same as mine. previouse owner had not drained water build up out of the fuel filter, in not doing this, the water had travelled with fuel through injectors causing surface rust inside which caused over fueling and very tappy engine. injectors knocking like nutts. the dvr( regulates fuel pressure) also built up surface rust inside causing the sensor to fail. i have replaced injectors and dvr sensor. and car runs sweet now. as for the egr, from experrience,, just onscrew the egr sensor and leave it onplugged, it will not affect your car not having it on.
if your engine is knocking its brains out after it getts warm and you are getting smoke from exhaust lack of power etc, then the egr is stuck open which will pump hot air from exhaust constantly into inlet housing.constant hot air .not good.