1.8T Going to Limp mode after hard run

[syphe]

hi all,
been lurking here for some time, but haven't really had much to contribute, but am having some problems and need a bit of advice, apologies for the long winded post, but thought I'd pour out as much information as I know about the issue instead of being rather vague.

I've got a 2003 Golf GTI with an AUM 1.8T, bought it in 2008 and within a month of owning it got it chipped by Basil from AutoPassion.
The remap has been fine since, however I have always had problems with the engine going into limp mode after going hard on the boost for a while, meaning either foot down well over the rev range, or over the course of a few hours on a long trip.
After turning the car off and on, the limp mode goes away, however as you can imagine gets bloody annoying when travelling.

By limp mode, I mean the car is limited to 5psi, but just until I restart the engine.

Took the car to Basil when I started having the problem, and he didn't really have any ideas other than getting is scanned for codes, at that point I had a knockoff vagcom usb cable in the post a few days away.
Since then every time I've scanned the engine for faults I've repeatedly gotten "17705 - Pressure Drop betw. Turbo and Throttle Valve (check D.V.!)".

Since then, i've replaced the DV, (710N came out, 710N back in), N75 valve replaced with a J valve, have spent a while checking pipes and hoses for leaks, bypassed the N249 valve (which made a huge difference to drivability, but didn't get rid of the code), and finally cleaned the MAF.

The car doesn't feel like it's missing power, so while it's been an annoyance, i've not gone to all the lengths to get rid of the code.

Anyway, now to the weekend, I decided to see if the problems with the car going into limp mode would occur if I unplugged the MAF, so unplugged it, went for a fairly spirited drive to see if limp mode would kick in, it didn't, however I did get a check engine light (MAF signal too low). After turning the car off while stopping at a store, got back in and limp mode hadn't kicked in, drove back home all the while giving it a few hard runs to see what happens, nothing, no limp mode.
Plugged the MAF back in, got the vagcom out, scanned for codes, sure enough, 17705 came back on after the engine started again, also had a code indicating the MAF sensor was too low. Cleared both codes and the CEL went away, so back to normal.

My assumption after this is that the MAF is poked, I've previously did some logging of the Airflow readings, and it seemed to indicate much less airflow than what it should have been getting, however I always took those readings with a grain of salt as doing a run through the rev range would cause limp mode to kick in, so wouldn't expect a great deal of airflow would be required for 5psi.

My question is, does this sound reasonable? I don't really want to get the MAF replaced without being somewhat sure that it is likely the problem.

Cheers

[RobClubley]

Sounds reasonable.
The 17705 code seems to be fairly common but hard to track down to a source.
I had it when I had a boost leak that caused my MAF to fail.

[syphe]

Cheers, I'll probably get it replaced tomorrow if I have the time, pretty sure the MAF is indeed gone, just wanted to have some reassurance.
Off to the stealers I go

[HandsomeDan]

Cheers, I'll probably get it replaced tomorrow if I have the time, pretty sure the MAF is indeed gone, just wanted to have some reassurance.
Off to the stealers I go

Can you not pick up a MAF anywhere else? Dealer will sting you.

[RS4]

We have a MAF here, needs to be on exchange for you dud one, but they are $250 each for a genuine one.

[80 Vert]

This code is also VERY common on chipped cars, if it appears after a cold start its the map at fault and even VW increased the difference tolerance on the last of the MK4's to overcome this problem.

[GTi101]

sounds just like my issue, except mine seems to be permanent 

[ddr77]

sounds just like my issue, except mine seems to be permanent 

Speak to the people who mapped it, they could be at fault or should put your original file back on as it should be covered under warranty.

[SAM_LOUI]

Wow, I have the exact problem.

I have a 2004 Volkswagen Golf GTI, AUM engine. And I've owned the car for just over 2 months now and the past owner got it tuned from Autopassion as well. The car was fully stock when I bought it, besides the tune done.

I wanted to install a boost gauge so I can keep my eye on the boost and if its holding pressure. So I installed a New South Performance boost gauge. And once installed I realised that my car would boost up to 17psi then would drop down and hold at 13-14psi. And eventually the car wouldn't boost above 5psi after a short drive or if I push the pedal down.

I've been doing a lot of research. And the things that have come up was to check the DV (which I have removed and checked if its holding pressure, and it is), Ive checked around the PCV hoses and even under the intake manifold. I thought everything was leading to one thing and It was the N75. I bought a brand new OEM N75 from VW and the car felt better. But the Limp mode seems to want to come back when it wants to.

Im not sure what to do now..

Oh and Ive also took my car to Supercheap to get it scanned couple times and the same code pops back in P0297 - Pressure drop.

[GLIDN]

with the 1.8T

if you have a failing MAF, failing 02 sensor, failing N75, low voltage to MAF, boost leak or weak wastegate. you will experience these issues.
First thing I recommend is testing wastegate pressure only, does it spike to 7psi and taper higher in the RPM band.

once you ruled out the wastegate is working correctly.
then move on to N75 and MAF

[SAM_LOUI]

with the 1.8T

if you have a failing MAF, failing 02 sensor, failing N75, low voltage to MAF, boost leak or weak wastegate. you will experience these issues.
First thing I recommend is testing wastegate pressure only, does it spike to 7psi and taper higher in the RPM band.

once you ruled out the wastegate is working correctly.
then move on to N75 and MAF

How do I test the wastegate pressure?

I took my car to "N S SPEC" in manukau and the guy removed the hose from the N75 that connects to the wastegate actuator and we took it for a spin. The boost spikes up above 20psi and it tapers as the rpm goes up. And i think it holds about 13-14psi? but not sure, as I was driving and had my eyes scanning for cops since there's a police station a kilometre away lol.

He suggested to install a boost controller or an electronic one. But I wasn't prepared to spend $400-$800 after seeing him look at the car for a good 5min and removed one hose and took it for a drive.

A good mate told me to get a good mechanic ( preferably someone who has a good knowledge about these car ) and have a look/drive/take logs and diagnose it for me then see where to go from there.

[GLIDN]

How do I test the wastegate pressure?

I took my car to "N S SPEC" in manukau and the guy removed the hose from the N75 that connects to the wastegate actuator and we took it for a spin. The boost spikes up above 20psi and it tapers as the rpm goes up. And i think it holds about 13-14psi? but not sure, as I was driving and had my eyes scanning for cops since there's a police station a kilometre away lol.

He suggested to install a boost controller or an electronic one. But I wasn't prepared to spend $400-$800 after seeing him look at the car for a good 5min and removed one hose and took it for a drive.

A good mate told me to get a good mechanic ( preferably someone who has a good knowledge about these car ) and have a look/drive/take logs and diagnose it for me then see where to go from there.

Something does not sound right, if the n75 is disconnected it should run wastegate only, which is 7psi.
reconnect everything back to stock. disconnect MAF and test drive car. it should now go to 7psi and no more.
If it still goes to 20psi, you have an issue with the tune or hardware.

shoot me a PM, if you'd like to me take a look at the car.
I can revert the vehicle back to stock if need be as well.