My 4.6 p38 lpg has developed a number of faults, when you come to start it it fires but doesn't start, this happens about 6 times then starts but is misfiring and is ticking over at 2000 plus. I have cleaned the maf and when I put a code reader on no codes, live readings show 8.6 on maf sensor. Only other problem is I have a rattle from centre exhaust.