Please help, mk5 gti no boosting properly

[gallardo1x]

hey guys for the past 2 weeks i’ve been trying to resolve this issue but after reading many forums and trying to diagnose i still can’t seem to find the fix.

I have a 2007 Gti that’s been loosing boost. when the car is barely at temp or after doing the first pull of the day it will boost all the way up to 14 psi for 2-3 pulls and then it will max out at 4-5psi after.
i can be driving it after a while in the night and it’ll randomly kick in to full boost for a moment.
i suspected it being a boost leak but i doubt the car would ever boost fully if it did.
i’ve also been looking into replacing the n75 considering that might be my last option.

if the wastegate was bad or turbo itself why does it sometimes boost perfectly and then not? it’s as if it’s in some kind of limp mode
i think my pcv is still working fine
i’ve replaced the dv with the newest rev
i have a cold air intake (new MAF)
3” Downpipe
pfr8s8eg ngk sparks, in the process of getting new r8 coils as i have misfire in cyl 1 and 4
i also have it on stage 1 united motor sports tune
about to do the cam follower on it too tomorrow


what other options do i have at this point?

 

[ROH ECHT]

For the PCV suspicion...disconnect here and blow into the tube after wiping it clean. It should be closed to contain boost. It opens when vacuum is applied...when the intake draws upon it.

Regarding the N75...disconnect its wire connector and test the N75's resistance. Should see 25 ohm. Replace the N75 if not at 25 ohm. VW has a ±5 ohm spec for it but it acts up when not at 25 ohm.
Look at the WG linkage where connected to the WGA rod. Just to be sure it is connected properly and not able to hang up in any way.
Double check all the boost hose connectors...just to be sure there's no leaking. Oily residue at a connection means the connector needs a new seal.
Is the new MAF a genuine OEM or an OE replacement? You may need to view its mass air data to confirm the new MAF is reporting accurate mass air.

 

[gallardo1x]

For the PCV suspicion...disconnect here and blow into the tube after wiping it clean. It should be closed to contain boost. It opens when vacuum is applied...when the intake draws upon it.
View attachment 203777

Regarding the N75...disconnect its wire connector and test the N75's resistance. Should see 25 ohm. Replace the N75 if not at 25 ohm. VW has a ±5 ohm spec for it but it acts up when not at 25 ohm.
Look at the WG linkage where connected to the WGA rod. Just to be sure it is connected properly and not able to hang up in any way.
Double check all the boost hose connectors...just to be sure there's no leaking. Oily residue at a connection means the connector needs a new seal.
Is the new MAF a genuine OEM or an OE replacement? You may need to view its mass air data to confirm the new MAF is reporting accurate mass air.

i’ll be checking everything you said tomorrow as it’s too late in the night now. so if the n75 is not at 25 ohm it’s forsure bad? i heard it’s a difficult job to do which is why i’ve been putting it off but at this point i just really want it fixed. the maf was from autozone. it was the only place the had it in stock near me and i really needed to pass smog at the time so i bought it link here for the one i bought

 

[ROH ECHT]

Unplug the MAF and test how it runs. (I would not use a re-manufactured one over the genuine OE sensor)
I know they are expensive but you should never need to replace it again. Do you have the original still?
Replace it with a genuine OE sensor when you can.
The N75 should be 25 ohm...swap it if not. I had one acting up and found it at 22 ohm. Yes, tough job because of the three small hoses.

 

[gallardo1x]

Unplug the MAF and test how it runs. (I would not use a re-manufactured one over the genuine OE sensor)
I know they are expensive but you should never need to replace it again. Do you have the original still?
Replace it with a genuine OE sensor when you can.
The N75 should be 25 ohm...swap it if not. I had one acting up and found it at 22 ohm. Yes, tough job because of the three small hoses.

unplugged the maf, no changes
no i turned the original in for a core refund
i’m trying to get my hands on a ohm reader now
this morning the car was boosting great again for the first 5 mins of driving and then it went back into the low boost mode. so frustrating.
hoping to get more progress tomorrow with diagnosing
i tried blowing into the PCV from the hose and i couldn’t get any air in so i’m assuming it’s still fine