P0299 P0171 Stock 2.0T FSI Throttle cuts

[jordan.a4]

Hi everyone. I've searched up and down the forum can't seem to figure the problem out.

Car: 2006 Audi A4 2.0T S-Line CVT

Background:
When I first bought the car about two years ago the owner complained about the car driving shittily, had some very bad hesitation issues and tons of codes. Well pulled the HPFP apart and voila the cam follower worn through. I have replaced the intake cam, high pressure fuel pump, cam follower, diverter valve (upgraded to the DV+), PCV, rear breather hose, air filter, MAF, cam position sensor, starter motor, and spark plugs (all brand new). That remedied the problem, the car drove fine for about a year and a 3/4 perfectly (slower than what online states (its a CVT I was getting 8.7s to 60 vs 7.8-8.0s to 60). I noticed the thermostat needed to be replaced when it got closer to winter time (got really cold in january-february not so much December).

Problem:
Soon as i took the car out and warmed it up, it had a throttle cut at high RPM (5000+ in 3rd gear+). When throttle cutting the RPM stays the same but the MPH moves extremely slowly or not at all, releasing the throttle and reapplying fixes it. When shifting manually sometimes when in gear and getting ready to race (3500-4000RPM at 15 MPH roll) it will not move RPM and "throttle cut". The EPC light comes on sometimes when it throttle cuts, but not all the time (about 60% of the time the EPC light comes on).

Codes:
The codes show up in three groups.

1st way:
P0171 system too lean (bank 1)
P0299 turbo/supercharger Underboost "A" condition

2nd way:
P0171 system too lean (bank 1)

3rd way:
P0299 turbo/supercharger Underboost "A" condition
P0171 system too lean (bank1)
P0341 camshaft position sensor circuit range/performance
P0011 (pending) "A" Camshaft Position - Timing Over-Advanced or System Performance (Bank 1)
P0089 (pending) fuel pressure regulator

The throttle cuts will happen without the CEL come on. I can drive around for 2-3 hours and have no codes but have throttle cuts.

Extra information:

It sometimes does not throttle cut but will have a hesitation at higher RPM. It will stay at 5900-6300 rpm for longer than usual (2-5 secs) and until it switches gear MPH won't move.

Fuel rail pressure is 1600-1700 PSI.

Catalytic converter is 700-800°C

Car NEVER fuel cut before thermostat change.

Different MAF doesn't help

If you are driving in an empty tunnel you can hear a distinct whistle with the turbo. My dad says it sounds fine but he is more of N/A educated. (Has over 30+ years in automotive industry multiple ASE's {also extremely busy so he can't really help me with this issue})

I had a friend drive behind me to see if anything is noticeable. He said it had a small backfire like noise and the exhaust smells like a school bus/test pipe when the throttle cut occurs.

Things that need to be done soon:

Timing belt

CVT tranny flush

Parts I think it might be:

O2 sensor
Thrust sensor
N75 valve

Sorry for the wall of text. Really did not want to post and have it be something simple or something already posted. Just haven't gotten anywhere these last few months and can't diagnose it. I have done about two oil changes since the problem started. Thanks in advance!

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[RakkCity]

Could be a boost leak, or a fuel problem, have you changed the fuel filter?

If you have VCDS, try logging the LPFP duty cycle, should be about 50% at warm idle.

Otherwise, might be looking for a boost leakdown test. Shouldn't have anything to do with your thermostat change.

[Van Black]

agree with ^ did you change the thermostat yourself? I worked on my car and somehow (probably) left one banjo bolt from the turbo loose; found it missing a while later after looking for causes for P0171.
p0171 is notoriously hard to diagnose since it could be a leak anywhere, which I tend to advise on since you get the underboost code. Also, I would check the plug to the ECU, I've heard people saying
moisture gets in and could cause that weird behavior

[jordan.a4]

Could be a boost leak, or a fuel problem, have you changed the fuel filter?

If you have VCDS, try logging the LPFP duty cycle, should be about 50% at warm idle.

Otherwise, might be looking for a boost leakdown test. Shouldn't have anything to do with your thermostat change.

I have changed the fuel filter. In the process of getting a VCDS. I will try to borrow my buddies smoke tester. Also haven't checked the waste gate actuator rod would that cause similar symptoms? Or a bad n75?

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[jordan.a4]

agree with ^ did you change the thermostat yourself? I worked on my car and somehow (probably) left one banjo bolt from the turbo loose; found it missing a while later after looking for causes for P0171.
p0171 is notoriously hard to diagnose since it could be a leak anywhere, which I tend to advise on since you get the underboost code. Also, I would check the plug to the ECU, I've heard people saying
moisture gets in and could cause that weird behavior

Will check the ECU plug. And will go through the intake and see if everything is all tight.

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[Van Black]

I have changed the fuel filter. In the process of getting a VCDS. I will try to borrow my buddies smoke tester. Also haven't checked the waste gate actuator rod would that cause similar symptoms? Or a bad n75?

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If the WG actuator is too tight it would cause underboost but I doubt it would lead to a Lean code since the MAF measures the air through the intake. P0171 means unmeasured air or too little fuel

[RakkCity]

If the WG actuator is too tight it would cause underboost but I doubt it would lead to a Lean code since the MAF measures the air through the intake. P0171 means unmeasured air or too little fuel

This. N75 or loose wastegate would cause the 0299 under boost but since you're getting lean fuel mixture I'm going with fuel/MAF related problem. Also if you haven't cleaned the MAF try doing that, a year and a half isn't too long but it might still be dirty causing faulty fuel maps.

[Van Black]

This. N75 or loose wastegate wood cause the 0299 under boost but since you're getting lean fuel mixture I'm going with fuel/MAF related problem. Also if you haven't cleaned the MAF try doing that, a year and a half isn't too long but it might still be dirty causing faulty fuel maps.

BTW, I'm also plagued by the dreaded P0171, but it's quite intermittent: it comes on mostly when I go over bumps and goes away after a while. Could it be a problem with the MAF, I've heard there was at some point a batch of crappy
sensors?

[RakkCity]

BTW, I'm also plagued by the dreaded P0171, but it's quite intermittent: it comes on mostly when I go over bumps and goes away after a while. Could it be a problem with the MAF, I've heard there was at some point a batch of crappy
sensors?

One way of determining a bad MAF is by disconnecting the harness and running the car on canned maps. If the problem goes away, chances are your MAF is bad or needs cleaning. Problem with your situation is you'd need to drive a while, and really wouldn't ever know for sure the outcome of the test since your issue is so infrequent.

If it's really not an issue, drive it until it gets worse. At that point, you can more easily diagnose the cause and won't waste time and money guessing what's at fault.

[jordan.a4]

One way of determining a bad MAF is by disconnecting the harness and running the car on canned maps. If the problem goes away, chances are your MAF is bad or needs cleaning. Problem with your situation is you'd need to drive a while, and really wouldn't ever know for sure the outcome of the test since your issue is so infrequent.

If it's really not an issue, drive it until it gets worse. At that point, you can more easily diagnose the cause and won't waste time and money guessing what's at fault.

Unplugged the MAF. Throttle cuts still occurred.

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[Van Black]

Unplugged the MAF. Throttle cuts still occurred.

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This one was intended for me. Just a thought, check your HPFP and harness to it. There's a solenoid that controls the HPFP flow, if it fails it could cause this

[jordan.a4]

This one was intended for me. Just a thought, check your HPFP and harness to it. There's a solenoid that controls the HPFP flow, if it fails it could cause this

Haha. I'm blind. Long day. It is a brand new HPFP. The new HPFP didn't come with a thrust sensor so that's the only old one.

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[Van Black]

Haha. I'm blind. Long day. It is a brand new HPFP. The new HPFP didn't come with a thrust sensor so that's the only old one.

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I'm on the other side of the planet my day just started

[jordan.a4]

I just received my VCDS. Is there any specific blocks I should target to diagnose this? The p0171 comes on at idle. The freeze frame data looked all normal.
Engine Speed: 744
MAF: 2.52 g/s
Throttle position: 17.4%
0 km/h

I also checked short and long term fuel trim. On a cold start after the RPM's settle down to 700-800 the short term fuel trim hovers around +20%. Long term was at +0.8%. Fuel Rail Pressure at idle was 700 PSI or so.

I got a ride to work so I can't post the exact freeze frame data logs. These were the readings I remembered off the top of my head.
Any specific blocks to measure would be greatly appreciated thanks!

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[Van Black]

I might be wrong, but the STFT looks way high. I remember reading it should be on a max of +/- 8%, or so. I get the same code sometimes and my trims are around 3% S and 0.7% L. Do you, by any chance, have a leaking head gasket?

[RakkCity]

Pull block 116 I believe it is, LPFP duty cycle. It should be 50-55% at warm idle. If it's more than that your low pump is bad and not able to supply enough fuel under load.

[jordan.a4]

Pull block 116 I believe it is, LPFP duty cycle. It should be 50-55% at warm idle. If it's more than that your low pump is bad and not able to supply enough fuel under load.

It was at 58-59%. Is that within spec?

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[jordan.a4]

I might be wrong, but the STFT looks way high. I remember reading it should be on a max of +/- 8%, or so. I get the same code sometimes and my trims are around 3% S and 0.7% L. Do you, by any chance, have a leaking head gasket?

Yeah, the short trim seems abnormal. As far as I know the head gasket is not leaking.

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[RakkCity]

That's a little high, try logging under some 3rd gear pulls, I believe it should stay under 80% at full load.

[Sanjman]

https://www.goapr.com/support/datalogging.php

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[Van Black]

Yeah, the short trim seems abnormal. As far as I know the head gasket is not leaking.

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Sorry, meant to say cylinder head cover gasket. Mine leaks and I suspect it might pull in unmetered air. But my code is more intermittent, it comes and goes.

[Sanjman]

Does it come after the car warms up? Maybe once the car warms up the gaskets may leak or hoses may start leaking?

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[jordan.a4]

That's a little high, try logging under some 3rd gear pulls, I believe it should stay under 80% at full load.

You guys wouldn't believe my luck. Some idiot crashed into a powerline and it's been on and off with power. I'll get the WOT blocks up as soon as I can.

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