Feel like I’m starting to bang my head against the wall this surging I keep getting when I put my fl1 td4 2004 under hard load image is showing the blue line is the inlet manifold pressure as you can see it’s up and down like a yoyo only does it if I accelerate harder than usual but if steady acceleration it seems fine and pulls ok any help or ideas would be greatly appreciated before I burn the bloody thing

First try unplugging the MAF sensor to see what happens, then maybe check the EGR and MAP sensor, as the manifold ever been cleaned on you FL how long have you owned it, after that do a leak back test.

Just a thought, but could boost pressure be dropping suddenly under hard acceleration because a hose is only leaking when pressure is at a certain level? You'd see black smoke from the exhaust though I think.