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Author Topic: Down on power…  (Read 939 times)

Offline JoshB

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Down on power…
« on: May 21, 2022, 03:21:34 pm »
So it started about 2 months ago, I didn’t really notice it at first, it was actually my other half that mentioned it felt slower than usual. Then one day going up a hill in 6th, I had to drop it into 5th to make it go… very unusual, but it still generally pulls quite well.
There’s a loud induction/whistling noise and the exhaust definitely sounds boomier.
I did have some gold/brass coloured flecks in my oil filter when I changed it last week (only about 5-6).
Cambelt was changed on Thursday and there’s no change.
I’ve inspected the DV (rev G) and PCV this morning, both fine.
Checked the inter cooler pipes and there’s no oil around the seals (looking toward the front of the car, the metal pipe on the left does move about in the clip, is this normal?)

Been out for some runs with the CarScanner app (sorry I don’t have VCDS) and come back with these.


It didn’t feel like I’d lost any boost, no kangaroo’ing etc, but I did occasionally feel the power go a bit wavey if you like. Seems to be making good boost still so I’m confused…

Any help is appreciated.
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Offline JoshB

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Re: Down on power…
« Reply #1 on: May 21, 2022, 05:31:30 pm »
Just been and took the air box off as I thought the whistling might be down to a cracked airbox. Nothing there.
It idle’s a bit erratically, hunts between 730 and 770rpm, is this normal? Occasionally drops to 690.
I tried disconnecting the MAF and the revs dropped, bogged down a touch but quickly went back and if anything idled better without the MAF. Brought the P0100 code up but cleared when I plugged it back in. Still no fault codes…
Oh and the “calculated boost” sits at -11psi at idle…
« Last Edit: May 21, 2022, 05:33:12 pm by JoshB »
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Offline ROH ECHT

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Re: Down on power…
« Reply #2 on: May 21, 2022, 06:32:22 pm »
Generally, when you unplug the MAF, you want to give it a few seconds to stabilize. If it does so...this points to an air inlet leak, or a failed MAF.

With a diagnostic tool, I.e. VCDS or capable OBD, you can check mass air report data and bring that data back to be questioned. You could also look for confirmation of air inlet leaks within the fuel trim data as instructed here;


K04 PLAY...K04 turbo/S3 INJ. & FMIC/FORGE FMTC, TB hose, & WG actuator/GIAC's H.O. K04 & DSG TUNES/AWE DV/NEUSPEED P-FLO,TURBO OUTLET & TB pipe/AUTOTECH hpfp/BSH Eng.&Trans Mounts/H&R ARB's/Whiteline Performance springs & W.A.L.K./ECS stage-3 BBK/BILSTEIN B8's...ZOOM'DIS...GIAC K04 tune-2007 Volkswagen GTI: 12.823 @ 112.050 MPH__Voting for my Dragtimes link: http://www.dragtimes.com/Volkswagen-GTI-Timeslip-25700.html?r=1

Offline Pudding

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Re: Down on power…
« Reply #3 on: May 22, 2022, 02:27:37 pm »
Exactly the same symptoms as mine. It's OK when in boost but the throttle response getting into boost and driving around town is horrible, it's like driving with the handbrake on.  It used to pull itself along easily on the motorway and like yours, I also have to drop down a gear just to maintain a constant speed.

I changed the turbo yesterday and it made zero difference.  I data logged MAF, boost, lambda, both fuel pumps, VVT, intake temp etc etc over a 30 min drive and absolutely nothing wrong, everything in spec.

The brakes aren't dragging.

I'm at a loss now. My next areas to try are replacing the green boost O-rings as the new turbo is a bit noisier than it should be, and checking the throttle body.  Whilst stabbing the pedal with VCDS up, I did notice a quite a bit of delay in the throttle body responding.

Partially plugged cat is another theory I have.

Bloody car  :grin:

P.S Occasionally mine tries to stall when pulling up to a junction then recovers, and this whole issue is intermittent as well.  Some days it's a missile, and some it's a complete slug. The fact it's capable of normal performance, even if temporary, suggests it's mechanically fine.  No idea what is going on as logging shows nothing and there's never any fault codes.  Tiny long term trims as well, <2%.

I'm nearly at the point of handing it over to a diagnostics place, but if I've fired the parts cannon at it, I'm not sure they'd find anything wrong either  :grin:
« Last Edit: May 22, 2022, 02:35:13 pm by Pudding »


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Offline ROH ECHT

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Re: Down on power…
« Reply #4 on: May 22, 2022, 05:07:28 pm »
Sometimes after much searching, some found tiny leaks in the oddest and unlikely places. From seams in the intake manifold to a brake booster diaphragm. Good luck with it, guys.
K04 PLAY...K04 turbo/S3 INJ. & FMIC/FORGE FMTC, TB hose, & WG actuator/GIAC's H.O. K04 & DSG TUNES/AWE DV/NEUSPEED P-FLO,TURBO OUTLET & TB pipe/AUTOTECH hpfp/BSH Eng.&Trans Mounts/H&R ARB's/Whiteline Performance springs & W.A.L.K./ECS stage-3 BBK/BILSTEIN B8's...ZOOM'DIS...GIAC K04 tune-2007 Volkswagen GTI: 12.823 @ 112.050 MPH__Voting for my Dragtimes link: http://www.dragtimes.com/Volkswagen-GTI-Timeslip-25700.html?r=1

Offline JoshB

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Re: Down on power…
« Reply #5 on: May 22, 2022, 07:03:51 pm »
I’ve ordered a new MAF sensor just in case, bang that in first then go looking for intake leaks.
I’m pretty sure it is an intake/inlet leak as like I say, it’s making the typical induction sucking/whistling noise.

Thanks for all the pointers!

Shame a new turbo made no difference to yours Pudding, as soon as you said about the turbo I started looking at K04 hybrids…!
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Offline G-olf

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Re: Down on power…
« Reply #6 on: May 22, 2022, 08:31:05 pm »
If they are full throttle logs in a single gear and i'm guessing they are, then maybe it looks like its dumping its boost? If this is the case then something must be telling it to do so.
As with most turbo cars,  expect a spike above target, perhaps dropping slightly below as the system gains control then to follow its requested reasonably close.
A bit like a torque curve on a dyno plot with an initial spike on spool
Perhaps try again with the requested boost also plotted on the graph?
I don't think it should jump around as much as that graph shows, someone on here will be able to advise you better  :happy2:
Is the map sensor reading something like you would expect?

Offline Pudding

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Re: Down on power…
« Reply #7 on: May 23, 2022, 08:38:44 am »
OK, so this is interesting.

This morning before setting off for work, I did a basic settings throttle adaptation in VCDS and the car was an absolute rocket ship for the entire one hour journey.  All of the symptoms described by Josh and myself, completely gone. It's the best it's driven in months.  It was like holding a dog back on it's leash. A night/day difference to how it was on Saturday & yesterday.

With the throttle being the primary driver input, it makes sense if that isn't functioning correctly it will kill the performance. I just need to figure out now if it just needs a clean, or replacement. Hopefully not the latter as they're about £300!

Based on this, I think I can safely out rule any general mechanical and fuelling issues  :laugh:

@JoshB it was worth doing the turbo anyway as the shaft had about 1mm of in-out play (the new turbo had zero play in any direction), which is why there was gold crumbs in the oil. It wouldn't have been much longer before the wheels started rubbing on the housing.  I also discovered 2 of the manifold to head bolts were finger tight, so no regrets there  :happy2:
Hats off the Borg Warner. The turbo put in 170K miles before getting to that point, not bad at all.

If your scan tool can do a throttle adaptation mate, give that a try.  If you have cruise control, see if the speed adjustment on that is more responsive than the throttle pedal, just as another experiment.

« Last Edit: May 23, 2022, 08:40:38 am by Pudding »


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Offline JoshB

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Re: Down on power…
« Reply #8 on: May 23, 2022, 09:58:30 am »
As I said I’m going to try and have a look round the inlets today, but as above, it’s like its struggling to breathe almost. Everything from the turbo side suggests it’s healthy, so the only other thing I can think of is fuelling. R-Tech did recommend I fit the stronger HPFP internals when it was remapped, but only if I went to map4/5, which I haven’t yet, I’m still at (or was) 250bhp/280ftlbs.

I can’t monitor fuel adaption unfortunately, it’s either HPFP internals or VCDS this month…
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Offline Pudding

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Re: Down on power…
« Reply #9 on: May 23, 2022, 10:27:27 am »
Internals won't hurt regardless, but VCDS is also worthwhile.  Its exactly what you need in situations like this, or maybe OBD11 as that can do a lot as well.

Well good luck with yours, it's gotta be something simple.

In an attempt to sort mine, I've ordered a used MK7.5 Golf R throttle body off ebay.  They're actually closer to £500 now, not £300.  Inflations a killer.








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Offline JoshB

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Re: Down on power…
« Reply #10 on: May 23, 2022, 02:04:31 pm »
I thought about the throttle body, like you say, there’s some pretty clean ones on eBay for £40-£50.
Had a good look round the engine this morning and there was nothing obviously leaking, but to be fair I didn’t spray any parts or poke around too much (don’t like running it without the airbox on…).
Did another couple of logs and every looks hunky dory… but the cars feels like it’s flat up top.



Just the bottom one, the short term fuel trims seem to be all over the shop, nice and flat under “normal” driving, but plant my foot and it sinks to -8% and then jumps to +5% when it catches up. And that’s the theme, it’s mostly between 0 and -10%. I’m hoping the new MAF cures it but I’m still leaning towards an inlet leak somewhere because of the noises.
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Offline rich83

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Re: Down on power…
« Reply #11 on: May 23, 2022, 02:15:56 pm »
Internals won't hurt regardless, but VCDS is also worthwhile.  Its exactly what you need in situations like this, or maybe OBD11 as that can do a lot as well.

Well good luck with yours, it's gotta be something simple.

In an attempt to sort mine, I've ordered a used MK7.5 Golf R throttle body off ebay.  They're actually closer to £500 now, not £300.  Inflations a killer.

I'm not sure the "parts canon" is the most economical way to find out what the issue is but it might work  :signLOL:

Mine sometimes feels like the boost comes and goes when on full throttle which is a bit sh*tty. I think the hpfp could do with replacing as I am putrefy sure if I logged it the fuel rail wouldn't quite be keeping up with the demand. That's what it feels like to me anyway.

Offline Pudding

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Re: Down on power…
« Reply #12 on: May 23, 2022, 02:50:19 pm »
I thought about the throttle body, like you say, there’s some pretty clean ones on eBay for £40-£50.
Had a good look round the engine this morning and there was nothing obviously leaking, but to be fair I didn’t spray any parts or poke around too much (don’t like running it without the airbox on…).
Did another couple of logs and every looks hunky dory… but the cars feels like it’s flat up top.



Just the bottom one, the short term fuel trims seem to be all over the shop, nice and flat under “normal” driving, but plant my foot and it sinks to -8% and then jumps to +5% when it catches up. And that’s the theme, it’s mostly between 0 and -10%. I’m hoping the new MAF cures it but I’m still leaning towards an inlet leak somewhere because of the noises.

The throttle body p/n has changed, yet again, to: 06F133062AG, making it the 6th revision!  I just got the newest one I could find on ebay.

You'll be lucky to see anything obvious.  GTIs like to hide the issue away for you to find like an Easter egg hunt, the little sh1ts!

10% lambda swings aren't too bad.  When mine does it's annoying thing, the short term swings were plus/minus 15-20%, which felt like horrible flat spots and wavering power delivery on gentle acceleration.

So yours is more of an issue up top, rather than down low?


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Offline Pudding

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Re: Down on power…
« Reply #13 on: May 23, 2022, 03:09:09 pm »
Internals won't hurt regardless, but VCDS is also worthwhile.  Its exactly what you need in situations like this, or maybe OBD11 as that can do a lot as well.

Well good luck with yours, it's gotta be something simple.

In an attempt to sort mine, I've ordered a used MK7.5 Golf R throttle body off ebay.  They're actually closer to £500 now, not £300.  Inflations a killer.

I'm not sure the "parts canon" is the most economical way to find out what the issue is but it might work  :signLOL:

Mine sometimes feels like the boost comes and goes when on full throttle which is a bit sh*tty. I think the hpfp could do with replacing as I am putrefy sure if I logged it the fuel rail wouldn't quite be keeping up with the demand. That's what it feels like to me anyway.

Tell me about it.  Not my preferred method of diagnosis!

I've been quietly looking to upgrade to a MK7.5 Clubsport or a TCR, but after looking at the prices of those things, I've decided to keep the MK5  :grin:  So really, what I've done here is a proactive canon firing to buy it some more life  :grin:

Yeah probably worth a logging session.  I got weird behaviour like that when I was mucking about with 2+ maps.  It was a mixture of K04 surge and fuel pump not keeping up, in spite of it being a Loba.


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Offline rich83

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Re: Down on power…
« Reply #14 on: May 23, 2022, 05:46:12 pm »
Definitely. Gonna re-buy VCDS ((stupidly sold it 6 years ago)) (gonna get the NET version) this summer so will be able to log it.