I replaced a dodgy TPS on a late D1 a few months ago, it had very similar symptoms. In that case it has a simple LPG mixer system that continued to work normally. With injected LPG it's going to follow the petrol fault. IMHO D1's are too primitive to make good use of LPG injection, but that's another matter. If you have a good TPS just swap it. New ones are seriously expensive, used ones appear on ebay occasionally.

