Hey all, iv a mk1 vrs 1.8, mapped to 190 thnow jus awaiting fmic and decat, cars runnin abit funny tho..

When am runnin half throttle av got loads of boost (gauge not accurate too) but gauge stays solid but when i push pedal to the floor it shudders and boost drops around 0.4bar (fluctuates) so easing on and off with pedal at the moment. Iv heard alot about faulty DVs causing this and the forge recirc has recently been fitted before i bought the car?

Either this or boost control?

All help is thankd greatly

ScallyVrsMk1

I'm having a similar problem, likely causes are an incorrectly tuned dv, I've put oem dv back on, improved slightly. You could try shimming up the spring in the forge or yellow spring but to be honest oem dv is fine.

Wastegate actuator, could be getting a weak spring or diaphragm perishing inside so it's unable to overcome pressure to stay shut. I have a refurbished STOCK replacement to go on but garage are reluctant as they think it's a turbo off job. I have read it can be done just by dropping turbo slightly, still not a job for me though.

N75, failures aren't common and would probably be more erratic boost on/off type thing.

Boost leak. Check pipework. Just before mine went into garage for actuator I noticed a small split in a short piece that comes out the intake into the one way valve. It's before the valve so effectively it's a leak from the manifold. I now hope it's this. It did seem quieter after I botched it with self amalgamating tape until I can replace it.

My car is making specified boost, then following down to 15psi, but then dropping below spec after 5200 revs. I suspect actuator and/or this leak for mine. I have a long thread running called 'dyno results disappointing and confusing' may be some info in there for you. Logging data helped me out a lot as I could rule out fuel pump and MAF and sensor related issues like that.