yeah sounds liek your hitting a boost limit.
limp home cut the ignition and when you try and give it any power it judders, sounds rought, spits, fars andwont give you any power at all.
as soon as ignition is switched off it seems to reset it self and it will run fine till the next time it over boost, but how long to leave it when switched off im not sure, try it your sellf, could be 1 min could be 30 mins..

but tbh it should not over boost at 8/9psi, you may have a map sensor fault, or maybe even a split vac hose somewhere?

give the plig on the map sensor a spray with some wd40, and check the vac pipe on it is free from splits, cracks etc, and being ofab, make sue the nipple coming off sensor isnt cracked around the base