crankshaft sensor code p0335 then p0336
hi all , alfa 156 1.8ts 2001 y, car just wouldnt start last week so i managed to get someone to plug diagnostic equipment in and it came back with code p0335 crankshaft sensor, i managed to get a replacement from my local motor factors, after much swearing and scraped arms/hands i have fitted it and the car fired up a treat, however now it really hesitates after about 2300rpm in all gears all the time, tried disconnecting the maf, no difference , so i have had the ecu read again and now it comes back with code p0336 , i haven't left the old oil seal in the crank sensor so i know its not that, any one got any ideas what could be wrong ? faulty sensor maybe? any one had any trouble using non genuine sensors ? also the airbag light is now on ?