there are some conditions where youll be in an inbetween 'phase'
(+ = psi/boost , - = mmHg/vacuum)
cruising at 85mph mine sits at -10 (i.e. its a part throttle)
general driving on light throttle I'm barely ever in +ve side
if you are on full or medium throttle you should be registering some + boost from any rpm.
going down a slip road under light throttle in 4th/5th I can make good progress and the guage registers around 5 psi
you cannot achieve large boost values at very low rpm (as the exhaust gases arent making the turbo spin fast enough)
if you were 'ragging' it , then I would always expect you to either be WOT(boost) or lift off (vacuum) , so yes you should see some boost all the time.
BUT if you go WOT in 6th gear from low rpm dont expect huge psi values.
below 2000rpm expect 3-5 psi then it should build quickly to peak around 2700 rpm (depended on the turbo you have)
as an experiment , try a straight empty road , be safe!, 3rd gear 50mph (what rpm is this)? and try going on and off the throttle to WOT , the guage should immediately go into the +ve side each and every time without fail, then back into -ve when you lift off
if it doesnt then yes you have a problem.
have you fitted an forge DV ?
do you have access to someone with VCDS who can log the car ?
let us know how you get on
