Had a chat to my mechanic friend, He reckons that since I upped my booster size, got bigger front calipers and rear disk brakes, And since Im still using the original 1.6l motor. That I am probably sucking most of the vacuum out from the intake manifold and into the booster. Thus giving me the answer as to why it tries (and sometimes succeeds) to stall when braking hard and driving, and it doesnt stall when braking hard and im idle.

Probably just need to get a mk3 engine in (which I was planning on doing). Hopefully that will fix it.

What you guys think?