I recently moved to France and discovered it would cost several thousand euros to register my 2007 tdv8 so decided to buy another for same money and keep my other for spares.
After finding a clean but high mileage 2007 tdv8 I collected it and started several hour return journey home.2 hours in I stopped for fuel.when I started the car and selected drive the revs dropped right down and it would only move at a snails pace.
While sat there with it back in park cursing the guy who sold it me the revs suddenly jumped back up and everything worked fine.
Strangely all the controls on dashboard don’t function in this state like radio etc
I’ve been running the car like this for a while now ,it works fine when engine cold but starts playing up when engine up to temperature.the gear changes etc seem fine for high mileage car.
Any ideas would be greatly appreciated on wether it’s something fixable or is my best option to swap out the gearbox off my other car.Cheers

With the dashboard problem, could be the ignition switch? Although don't know why that would cause the revs to drop ...

Thanks for the reply.i hadn’t thought of checking ignition,will look into it.cheers