hi Guys,

So recently my polo gti 9n3 starting acting faulty, when I accelerate full it only boosts up to 0.4 bar, but when I accelerate halfway it slowly goes up to 0.9 bar peak, changed the turbo 2000kms ago and previous turbo peaked at 1.3 bar, also it became very heavy on fuel and backfires and switches off in traffic,

any ideas what could be wrong? does it need a remap and if so who do you recommend?

Try a different fuel pressure regulator or check pressure lines going to it they small diameter pipes and enough movement could tear the hose.

I'd check all the plugs and confirm that they're plugged in properly, i.e. Map sensor, Maf sensor etc. It could be a mechanical issue or electrical, so it's a good start to check all your harness/sensor plugs and hoses etc.

Next I'd check for any boost leaks. Who rebuilt and refitted your turbo if I may ask?

Okay im not sure how to check pressure lines lol , if it is overfueling could it be that my plugs need to be changed? and a ex vw technician just replaced the turbo i did not repair it.

As above and check also

1.N75 Solenoid. perhaps it was reinstalled incorrectly.
2. Inspect Down-pipe and and manifold for no leaks.

All else fails, have the car scanned , hopefully it points you to the right direction.