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Old 08-05-2017, 01:31 PM   #1
Octane
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WOT bucking/hesitation under load

Hi everyone,

I have a completely stock 2012 GTi 6MT with 70,000km. Bought it last year with 55,000kms as a certified pre-owned car. The dealer did the 4-year service, replacing plugs and coils at that time and it has been running great since then until recently.

I have been noticing a very brief <1 second bucking/hesitation sort of feeling under full load, wide open throttle conditions. Presents itself mostly in 4th, 5th and 6th gear accelerating from cruising speed. For example if I am driving at 70km/h in 6th gear and roll on the throttle up to highway speed, the power will cut out for a split second around 2,000rpm as the boost just starts to build and pulls fine after that. The other time I have noticed it happening is when slowing for a red light on the highway, downshifting to 4th gear and slowing down under engine braking - then going back to throttle when the light turns green, 50-70km/h. The car will stumble for a second then start to accelerate. These symptoms are more prevalent when going uphill or carrying passengers (higher engine load). There is no specific conditions that will reliably cause this to happen every single time, but in general that's when it tends to appear.

Just had a 6-month service, oil change and inspection done and had the mechanic drive the car. No check engine light, but they scanned it anyway and drove the car with the scan tool hooked up and didn't note any faults. I drove it around my for a while last night and it happened once under hard acceleration in 3rd gear. The common cause seems to be a sudden application or increase of throttle pressure.

Any advice you could give me would be greatly appreciated. I'm usually pretty good at diagnosing these sort of things but I'm at a loss here. Cheers.

Last edited by Octane; 08-05-2017 at 10:30 PM.
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Old 08-06-2017, 02:46 AM   #2
Carlosfandango
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Quote:
Originally Posted by Octane View Post
Hi everyone,

I have a completely stock 2012 GTi 6MT with 70,000km. Bought it last year with 55,000kms as a certified pre-owned car. The dealer did the 4-year service, replacing plugs and coils at that time and it has been running great since then until recently.

I have been noticing a very brief <1 second bucking/hesitation sort of feeling under full load, wide open throttle conditions. Presents itself mostly in 4th, 5th and 6th gear accelerating from cruising speed. For example if I am driving at 70km/h in 6th gear and roll on the throttle up to highway speed, the power will cut out for a split second around 2,000rpm as the boost just starts to build and pulls fine after that. The other time I have noticed it happening is when slowing for a red light on the highway, downshifting to 4th gear and slowing down under engine braking - then going back to throttle when the light turns green, 50-70km/h. The car will stumble for a second then start to accelerate. These symptoms are more prevalent when going uphill or carrying passengers (higher engine load). There is no specific conditions that will reliably cause this to happen every single time, but in general that's when it tends to appear.

Just had a 6-month service, oil change and inspection done and had the mechanic drive the car. No check engine light, but they scanned it anyway and drove the car with the scan tool hooked up and didn't note any faults. I drove it around my for a while last night and it happened once under hard acceleration in 3rd gear. The common cause seems to be a sudden application or increase of throttle pressure.

Any advice you could give me would be greatly appreciated. I'm usually pretty good at diagnosing these sort of things but I'm at a loss here. Cheers.


Maybe try a throttle body adaptation (TBA) using VCDS, I know people will say the adaptation is done every time you cycle the ignition but from my experience this is not true based on watching the 060 engine measuring blocks while doing this, I used to have a similar problem of bucking but at low speeds (1st gear) in traffic, particularly when stop/start-moving/crawling up hill, I had a stage 1 tune done some time a go that appeared to improve this but had to have the tune removed for other reasons, at the moment I'm stock and have recently had a new head fitted (which is great and the engine is sweet) but over the last few weeks in particular the bucking has returned but worse! It occurred to me a couple of days ago that maybe I should try the TBA again and can say with hand on heart it has completely cured it, there is zero bucking and the shifting is silky smooth in all driving conditions (Due to correct throttle position at the correct times I presume) the car is clearly more eager too which is not a placebo I can assure you! Give it a go if you have VCDS or find someone who can for you, it only takes a couple of minutes to complete and if it doesn't improve things then no worries! Nothing ventured nothing gained as they say!
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Old 08-06-2017, 05:58 AM   #3
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coil packs/plugs
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Old 08-06-2017, 07:04 PM   #4
Octane
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coil packs/plugs
I think you might be right. I was thinking it was fuel/boost related or possibly something to do with the clutch. It's been driving me crazy so I went for a long drive today and tried my hardest to get it to throw a code or something definitive to happen. Finally it totally let go while merging onto the highway and the CEL was flashing, really bad sound and vibration basically running on 3 cylinders. CEL didn't stay on but I do have an EPC light on the dash which looks like it is likely coil packs. Took about a month from the first symptoms appearing to this, so it died a pretty slow death. I'm taking it in to VW again and they should be able to sort it out. Thanks!
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Old 08-07-2017, 02:23 PM   #5
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Quote:
Originally Posted by Octane View Post
Hi everyone,

I have a completely stock 2012 GTi 6MT with 70,000km. Bought it last year with 55,000kms as a certified pre-owned car. The dealer did the 4-year service, replacing plugs and coils at that time and it has been running great since then until recently.

I have been noticing a very brief <1 second bucking/hesitation sort of feeling under full load, wide open throttle conditions. Presents itself mostly in 4th, 5th and 6th gear accelerating from cruising speed. For example if I am driving at 70km/h in 6th gear and roll on the throttle up to highway speed, the power will cut out for a split second around 2,000rpm as the boost just starts to build and pulls fine after that. The other time I have noticed it happening is when slowing for a red light on the highway, downshifting to 4th gear and slowing down under engine braking - then going back to throttle when the light turns green, 50-70km/h. The car will stumble for a second then start to accelerate. These symptoms are more prevalent when going uphill or carrying passengers (higher engine load). There is no specific conditions that will reliably cause this to happen every single time, but in general that's when it tends to appear.

Just had a 6-month service, oil change and inspection done and had the mechanic drive the car. No check engine light, but they scanned it anyway and drove the car with the scan tool hooked up and didn't note any faults. I drove it around my for a while last night and it happened once under hard acceleration in 3rd gear. The common cause seems to be a sudden application or increase of throttle pressure.

Any advice you could give me would be greatly appreciated. I'm usually pretty good at diagnosing these sort of things but I'm at a loss here. Cheers.
In addition to what others mentioned, I've heard of misbehaving N75 valves causing issues like this too. For example, if the N75 is slow to respond to ECU inputs you may be getting an overboost spike that the ECU is pulling timing or modulating DV/throttle plate to protect for.
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Old 08-07-2017, 02:24 PM   #6
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Quote:
Originally Posted by Octane View Post
I think you might be right. I was thinking it was fuel/boost related or possibly something to do with the clutch. It's been driving me crazy so I went for a long drive today and tried my hardest to get it to throw a code or something definitive to happen. Finally it totally let go while merging onto the highway and the CEL was flashing, really bad sound and vibration basically running on 3 cylinders. CEL didn't stay on but I do have an EPC light on the dash which looks like it is likely coil packs. Took about a month from the first symptoms appearing to this, so it died a pretty slow death. I'm taking it in to VW again and they should be able to sort it out. Thanks!
Just reading this, coilpacks have been known to fail on stock applications. Skip the dealer, get a set of R8 redtops and you're set.
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Old 08-07-2017, 02:50 PM   #7
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Just reading this, coilpacks have been known to fail on stock applications. Skip the dealer, get a set of R8 redtops and you're set.
this. Don't even bother with a dealer. This is one of the simplest repairs.
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Old 08-07-2017, 03:51 PM   #8
Octane
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Thanks guys, I have been reading about that... I'll let VW fix it this time under warranty just to get me back on the road, and I'll order a set of R8 coils in the meantime to install whenever it inevitably starts acting up again.
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Old 08-07-2017, 04:06 PM   #9
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Thanks guys, I have been reading about that... I'll let VW fix it this time under warranty just to get me back on the road, and I'll order a set of R8 coils in the meantime to install whenever it inevitably starts acting up again.
Also a good call.

You said they replaced the coils like 15,000 km ago? That seems like a really short lifespan for new OEM coils. Maybe keep the redtops in the car with you at all times just in case :-P
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Old 11-09-2017, 11:17 PM   #10
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Were you able to find a solution? I am currently suffering the same issues, except APR stage 2. Emailed APR and no response thus far. No codes, no stored codes via VAGCOM, Data logging seems fine for boost no suspecting a boost leak, and the clutch doesnt show the classical signs of slipping.
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Old 11-09-2017, 11:46 PM   #11
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Possible vac leak, check pcv valve as that can cause major leaks you don't see, as mentioned the plugs and coils, carbon build up is also possible as the a or becomes much more turbulent at high rpms with asll that crap in the way.
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