2000 Mercedes Benz V280 Engine misfiring

Hi gentlemen technicians,
I own a Mercedes v280 with factory fitted lpg system
Ihave never used lpg since bought three months ago
I have a misftre I hope my info is correct as I am going on the say of my mechanic friend who has been working on the vehicle in question.
I bought the v280 3 months ago without the misfire, two weeks later developed my current misfire problem.
Ihave spent £600. With my mechanic doing the work that I was advised to do my an exmercedes mechanic
This merc mechanic gave me a diagnostic which didnt do well in identifying the specific problem, a couple of codes were p1108 continuous positive, p1010 lamda sensor signal wire, p1037, idle speed control adaption,
p1319 minimum stop throttle valve sensor and some referance to a faulty lamda sensor? The same mechanic told be to start from the ground up so I changed plugs ht leads, my mechanic checked compression ok injectors ok? Bought two from breakersyard. Com and my mechanic changed an existing duff one of the two I bought, new injector ring seals, new manifold gaskets, fuel filter, I bought a cheap ign coil to test existing ok, I have not tried air mass sensor yet, well the costs are becoming an issue

I am at the point where I wonder if I have lost the vehicle, sold a melon so to speak, Could the timing chain be the problem I dont know Please can you help I am more than willing to donate but have problem transfering money over the net at this time, give me your address and I will send you donation cheque
Thanks gents hope you can help in some way, curiuos to read any possible replies Regards Gerry