Volvo V70(P2) 2006 - stepper motor fault (or not?)

[SquareOne]

Hello everyone

About 3 months ago my Volvo started to die out while driving on CNG. After that I started to comb through different forums and they all pointed to one component - the stepper motor.

Before I start the search for a new one (as I've understood by now they are quite rare and a new one costs around 800€) I decided to ask you guys for some insight whether my fears are true or not, so here goes.

Behavior: Car starts up fine and switches to gas normally, then after about 5-7 minutes dies out on gas and doesn't automatically switch to petrol (a real pain and embarrassment when I happen to be at a red light when this happens). After switching to petrol and starting the car (sometimes might take about ~10 seconds of cranking to get it started) if I were to switch it to CNG it would also die, the only way of getting it back on gas is to either let the car sit for an hour or to drive for a bit and try again (classic stepper motor issue as far as I can tell), but...

When I drive the car on petrol for about 10-15 minutes until it gets warm and then switch to gas the car would make the switch and drive without any problems until performing a restart. Then almost immediately after turning the car on again with gas mode switched on it would die out. The only remedy to that is to start the car in petrol mode, drive for a minute and then switch to gas, then it would again work without cutting out. Seems strange to me...

Also after the cut off has happened, starting in petrol mode and switching to gas there would be a clunk and a hissing noise from near where the regulator lives, until the engine dies out.

Any thoughts on this?
-Karl