VW lt35 51 reg engine nightmares

[Siosal]

Hello folks.

I've got a VW LT35 2.3 Mercedes petrol engine with an LPG conversion. I bought the vehicle 300 miles from home and it cruised on the motorway without any problems. Problem was, the revs died and it stalled every time you took your foot off the throttle.
I took it to my local commercial dealership to get fixed. £900 later and a new throttle body had been fitted. Great, no more stalling.
Gradually from then on the VW has lacked power up hill and even on some flats, with fuel consumption ridiculously high. This was diagnosed as a faulty exhaust valve's flap jamming. £300.
Less noise from the engine now but no greater performance. Faulty MAF was next suggested, only to find that the 2.3 Mercedes petrol engine doesn't have one. Yet another diagnostic test and an oxygen sensor fault was throwing up faults with 2 out of the 4 cylinders, so £200 was spent and a new sensor was fitted.
Just as bad as ever. I've now been advised that the turnover valve may be causing the problem. Please could somebody help me out here because it's obvious that nobody from the dealership has clear knowledge of my engine as they all describe it as rare. I'm paying out sums of money with no end result. I can't help but think that the new throttle body has caused this, but the dealership disagrees and seems to want to work it's way around my entire engine.
Thanks in advance for any help.

Siosal

[vw workshop]

I bet that there isnt a VW dealer in the county who has worked on many of these.Everything is diesel.Is this one of the Tickford converted vehicles for Tescos ? (ryder vehicle contracts) if so they gave a lot of trouble when new,the usuall lpg backfiring ect. i dont think the throttlebody is the cause of the fault and i recon the dealership is trying hard to cure it but it isnt (the lpg conversion) even vw stuff and they would have no tec. backup.i used to do LPG conversions about 10 years ago and remember having a few vehicle with forward facing air intake pipes for the airbox (where the air filter is) having a fault like yours. The foward motion of the van used to cause the incoming air to weaken of the lpg mixture and cause it to stall,the cure was to place a baffle a couple of inches in front of the air intake.The intake isnt restricted but it stops the air blowing the candle out ,lol.
You may be better trying an lpg specialist ?

[Siosal]

Thanks for your reply.
Tickford yes, converted fo Glasgow Council. The van runs exactly the same on petrol as it does on LPG. I ran it on petrol for a month solid which turned out to be very costly. I am restricted to 2nd gear going up hill around town and can't do above 40 up hill on a motorway. Pulling away in 1st and then into 2nd is no problem at all. Even 3rd can be nice and pokey when on a flat or downhill - it's when I want to go up sometimes even the slightest of gradients that all power above 2nd gear is lost.
If I'm running the van on petrol all of the time, I'm assuming any fault with the LPG will be irrelevant ?
Cheers for your help, as you're the only person I know that has any idea about my engine

[vw workshop]

Does it still cruise on a flat motorway ok ?i.e. is the fault only happening under load