Right, I'm now wishing that i'd bought a Scooby. my N75 is plumbed as follows: middle port to actuator, long one to tip, short one to charge. If you follow that black pipe that runs from the top of the inlet manni, through the N/R valve and come to a t piece just below where Danny's N75 is in the picture. I have plumbed the Combi valve here cos i don't know where it's meant to go.
my plumbing has been simplified to try and identify any issues.
It's now: FRP to manni. other manni nipple to d/v via black and white check valve. (the boost gauge is t-pieced into this line). N75 to charge, actuator and tip. the t-piece that i described earlier is linked to combi valve.
I've now hit limp mode, and i'm fuming. I wish i'd never bought this car.
I'm in Barnsley, if anyone is nearby so i can take a look at theirs, or try their n75 or even MAP sensor.
I've checked as many pipes as i can see and have found no splits.