Engine management light comes on sometimes, vehicle runs & drives ok but tick over eratic. Pull off main feed pipe to secondary air pump, vehicle ticks over properly, lambar sensor ok but then air mass sensor starts not reading correctly. Have already replaced lambar sensor. If the secondary pump main feed pipe is re-connected correctly the air mass sensor starts reading properly but the car ticks over rough and the lambar goes out of specification. Has any-body any ideas as to what I can try next?