Bongo Fury

Hi all was wondering if anyone can help me sort my bongo..its a 1999 2.0 petrol on lpg
It starts up ok get less than a mile down the road and it starts running rough sounds like its off on a cylinder, if you come to a junction or stop the engine usually stalls if you start it again most of the time it starts up and runs fine for a bit sometimes only couple of minuets then does it again if when started up again and it runs rough if you stop it turn ignition on and off a couple of times it starts up fine again then does it again...
so far i have changed,
Ignition module
Coil
Rotter arm
Distributer cap
plugs
leads
lambda sensor
ive checked all the pipes for cracks splits checked wiring im now now idea with it
its got a multi point lpg conversion on it and does the same on petrol and gas so certain its not fuel related..
Could the idle control valve cause it to seem like its off on a cylinder?
ive tried pulling plug leads off when it does it but no cylinder seems to make any difference
any help would be much appreciated

Sorry I can't help you out, but if it's any comfort - you are not alone! We have something very similar with our 1999 lpg V6, although don't have any (very few) obvious mis-fires.
About 500miles ago we replaced all the parts you mentioned except the Lambda and it seemed sorted, but yesterday on the way home from Bongo bash, on Burford High Street the engine quietly died but (thank heavens) immediately restarted. Died again as I exited A40 and rolled to a safe halt....... one more unplanned stop before home where I let the engine idle and the rev counter showed the engine hunting up and down.

I keep a record of mpg and that has dropped by 4 - 5mpg. I'll probably get a Universal (based on price) Lambda fitted as the symptoms seem like it might be connected but really it's only a punt and if it didn't fix yours'.
I've always thought the van badly under powered and it's been suggested the cat is choking the exhaust - I've decided to test that possibility out. Maybe there's some connection?

update. I've just been under the bongo glowering at the Lambda (hoping to shame it into performing) and detected a small exhaust leak the other side of the cat. On another car, a similar leak caused 'hunting', so I'll sort the leak next and see if the engine dying problem is sorted before spending on anything else. Have you checked for exhaust leakage?