Introducing myself (PoloGT) and some questions.

[PoloGT]

It's the amount of gears? Automatic Gearbox and then the amount of gears as I can find on Google. AG4 in that case

[brianh]

I think thats one way to tell yes, I think the AG5 may be a tiptronic type one. Doesn't help then. Only other thing i can think of outside of whats already been suggested is if the idle control valve is sticking (on the inlet manifold) That generally will stick worse when its cold. May be worth removing it and giving it a clean?

[PoloGT]

Hmm.... That could be. If it sticks and releases it will be as sudden as experienced. Also. If it's not working correctly the LPG system will simply adjust. But also adjusting the valve again this explaining the slight problems I experienced shortly after switching back to petrol when engine is warm.

I'll  clean it and let you know. Feels a bit like coming full circle here if this is the reason . Thanks again. I'll let you know what I find

[brianh]

It tends to be one of those things that fails but doesn't give a fault code when it does as well, you just get the cutting out, but yours may be sticking at open rather than closed or somewhere between, just causing lack of acceleration. Though I'd check that hose Chris mentioned as it does sound a bit like a vacuum leak problem to me.