Basically I've got an Octavia vRS, recently its started underboosting, feels like theres no turbo on it at all.

I've got a HKS blow off fitted that usually whistles, but when its underboosting it just makes a psssssssssss sound like theres no pressure there.

IF you turn the car off and start it back up it disappears, but it can start doing it again after a while, although sometimes it boosts fine for hours/days etc.

Just wondered if anyone had any ideas what it could be?

Ta

Your blow off valve is sending the car into limp mod would be my guess.

:iagree:

they dont like atmospheric ones do they!! they work better with re-circ type fitted

I had similar intermittent limp mode problems recently that were cured by removing the induction kit and fitting a new MAF. You may want to get a read out of the fault codes you probably have.