W203 2002 M111 P0172 code issue

[chrisbeeching]

Hi All. I live in Alderney - a land devoid of main dealers, and a mile wide and three miles long. I have a 2002 W203 2.0 Kompressor estate with an M111.955 engine. Only code reader is the Autel AL319. Car has a gas conversion (LPG) but as the issue is identical on both fuel systems I don't suspect fuel 'supply' to be the issue. Car keeps throwing a P0172 code. Interestingly the reader says it's running rich at lower revs and lower loads (less than about 35%) and lean at higher revs and higher loads (50% up). STFT at idle is initially around the -2%, then drops like a stone. Hill climbing at higher revs and higher loads STFT is around +10%. LTFT is sitting around the -21%. Have checked all vacuum hoses (no leaks found, and all in good condition), new genuine MAF sensor (horrendous price plus shipping to this tiny island), (no change), engine coolant sensor seems to reflect actually running temperatures and cooling fan cuts in for full speed at 96 degrees, cools to about 89 then climbs again. Have two new O2 sensors on their way. Have noticed some threads on other forums have suggested the AIT sensor may be faulty... not checked it yet but could that throw the code? Running issues are lumpy idle and pull-away, higher than expected fuel consumption, and hunting (when in park) when 'hot' (i.e. after a long period of idling). Anyone have any insights? MB Star not an option - cost of shipping it plus a 'man' to use it is prohibitive - as is shipping the car off-island. If more info is needed please ask, but any suggestions gratefully received.