p38 problem running on lpg

hi i am new to this site so can any one help i have spent about £3000 intotal on an OMVL DREAM multipoint system.
To try and make my 4L SE P38 RUN well
the story is i got it converted by A1 auto gas liverpool never run right took it back several times then went on holls came back and firm had closed up so i have had it to several firms all say with a shake of the head they are taking on someone elses work i pay out and still runs rough .
Some have said its the car poss air flow meter but had new first thing, one know what it could be

A bit more information may help, does it run ok on petrol, what are the symptoms, this site may help you..............................
LPG Discussion Forum

Don't know whereabouts you are but also found this........
LPG Auto Conversions Contact Details

hi tervueren it does run ok on petrol but tick over a little low.
symptons are on idel surges then cuts out when comming to a stop also runs ok some times then when worm will run rough for no reason also runs fine then starts playing up again
i have looked at the lpg site before thanks any way