Check the actuator isn't stuck and also check for boost leaks, could be leaking out of any of the connections.

If it's permanent low power it's probably worth checking the maf with vagcom too

 

Just came across this thread (http://uk-mkivs.net/topic/34834-vnt-tdi-turbo-how-to-adjust-actuator-cure-boost-problems/)

Can someone please explain how i do step 1 (using VAG COM log block 11 from 2000rpm to 4000rpm in 3rd gear on a flat straight bit of road)

Also can i do this step with the vcds lite software or do i need to pay for the full version??

Took the car out to a flat straight bit of road and in 3rd gear got to 2000 rpm then gave 100% throttle, Got to about 2800 rpm then a sudden drop in power,

Turned off the ignition then started again then i seemed to have a small amount of boost again untill a past 2800 rpm then it died off again.

Does this narrow down the fault any?? If I could figure out how to do a road test with VAGcom then i might know a bit more..

 

If youngo easier on the throttle does it keep it's power? Like is it just if you boot it you lose power?

 

If youngo easier on the throttle does it keep it's power? Like is it just if you boot it you lose power?

Yeah mate that seemed to be the case, I will double check it though

 

Yeh check and see, if the power just suddenly goes but comes back after a restart then it's limp mode but if it's low power all the time it's different or can be, there are some things that cause both.

 

Yeh check and see, if the power just suddenly goes but comes back after a restart then it's limp mode but if it's low power all the time it's different or can be, there are some things that cause both.

Could doing the VAGcom 3rd gear test narrow it to a single cause?? I think its the actuator or the MAP sensor, just dont wanna buy one then it be the other at fault, Any way to find out for sure what's causing it?

 

Don't buy either yet, it's rare for it to be the map sensor though. Take the vac pipe for the actuator and suck on it then stick your tongue on the end to see if it holds vac, get a screw driver down the back onto the vnt lever the actuator connects to and give it a push down to see if it moves ok, it's under spring tension but that's all. Take off the elbow boost pipe that goes to the egr and check it for gunk, the intake can get pretty clogged. Check all the boost pipe connections for oily mess which could point to a boost leak. Plenty to try before buying anything.

You know the boost is low at least, now just need to find out why but it's mostly getting your hands dirty to figure it out.

 

Ok so the actuator doesn't seem to be seized, When i suck on the vac pipe it moves the actuator and it holds vac and stays in position when i cover the end of the pipe, Also i got MAF sensor cleaner today and tried cleaning it but still nothing, Also tried swapping it with a know working one from a friends car so i don't think it's at fault, Replaced the remaining few vac hose pipes i could see and still i get limp mode in 3rd gear at medium to high revs???, :-o

 

Just google the code P1556 bud, you'll get shed loads of info on it and things to try, there's a lot of tdiclub links, good site for info