Engine Performance problem
2003 Alfa Romeo 168 s 6 cyl Front Wheel Drive Manual 243000 miles
I blew my car up and needed a new engine. My mechanic has replaced the engine, cambelt, spark plugs all filters etc etc. My car had an engine light come on with code p0139, p1172, p1175 with is a lambda1 and mixture sensor. We had the sensor replaced and the light has gone away. However all the time my car has been hesitating through the rev range, pretty much stalling and then going constantly. You can really notice it when accelerating from 3-4k rpm.
I turn my air conditioning off and it doesn't hesitate as much, but this could just be a strange conicidence.
Any advise on what we should be looking at or ways to fix this would be awesome.