Strange

As said above the reason i know if it stalling, is because when the cap is removed that big hard plastic pipe that runs from the emission control filter to the air box allows a big air leak to enter the system after the flap which stops fuelling to the engine.

I did have an RS i got proper skanked on, that was standard, but that ran without the cap on (also blew the cap off the first time cos i went for a test run without the bonnet on and saw it fly off PMSL )

That car was fucked though, if i ragged it down the road you could follow the white trail of smoke to find me