Genuinely baffled, I've never heard of this happening before
The only 2 things that come to mind, is something has chewed through the wiring loom somewhere, or it's some sort of a problem with the components involved in idling.
When going down a hill almost all engines now will cut the fuel to the injectors and the engine is kept going on the momentum of going downhill, the clutch is engaged (driving) when this happens, except the wheels are driving the engine instead of the engine driving the wheels - when you touch the gas again or dip the clutch the fuel begins to be added to the cylinders as normal. If it's happening when you reach the bottom of the hill, it's possible something is going wrong with this system - but I don't even know what the components of it are that could have broken or how that could show as something electrical
Hopefully someone comes along with a bit more knowledge than me
