S3 Issue - Sticky Falling Revs with Shudder - Help Needed

[Silky-S3]

Hi guys,

I’m hoping you can help...

My S3 has suddenly developed a strange shudder/noise when the revs are falling and falling through about 1,500 rpm. It only happens in neural, when the revs are falling after rev’ing the car (zero throttle). It gets to about 1,500 rpm, the revs suddenly fall slower (like going through a sticky spot) and there is a slight shudder/noise and then it goes away again. Happens every time. Can’t feel it when driving and it pulls very clean all the way from 0 rpm to the redline.

Anyone got any idea what it could be? I’m thinking vacuum issue, or some sort of air leak? No faults on VCDS by the way.

Thanks!

 

[warren_S5]

Hmmmmmmmmmm

Initially I was thinking air leak, but .... further questions:

1) What mileage are you at?
2) Who fitted your fuel pump (and when) / was cam follower checked at same time?
3) Have you checked to see if the ITG hose that that attaches to the turbo (that goes down back of engine) is clamped properly - preferrably with the OEM hose clamp that is self adjusting?
4) Have you ever changed the plugs?

For some reason MAF came into my head but dont think it will be. Peolpe mention smoke testing for air leaks on here, but to date I've never found anyone who professes to be able to do it.

 

[Silky-S3]

Hmmmmmmmmmm

Initially I was thinking air leak, but .... further questions:

1) What mileage are you at?
2) Who fitted your fuel pump (and when) / was cam follower checked at same time?
3) Have you checked to see if the ITG hose that that attaches to the turbo (that goes down back of engine) is clamped properly - preferrably with the OEM hose clamp that is self adjusting?
4) Have you ever changed the plugs?

For some reason MAF came into my head but dont think it will be. Peolpe mention smoke testing for air leaks on here, but to date I've never found anyone who professes to be able to do it.

Thanks for your quick reply Warren:

1) What mileage are you at? About 9,000
2) Who fitted your fuel pump (and when) / was cam follower checked at same time? FP internals fitted by myself along with new follower (old one had no wear), fitted about 3,000 miles ago
3) Have you checked to see if the ITG hose that that attaches to the turbo (that goes down back of engine) is clamped properly - preferrably with the OEM hose clamp that is self adjusting? Not yet, will check this. Gonna try to refit it with the OEM clamp this weekend.
4) Have you ever changed the plugs? Yes same time as FP internals, 3,000 miles ago.

Thanks

 

[warren_S5]

Did you fit HPFP in a clean environment (as much as possible in real world), and then use the recommended lube to bed it in?

Might be worth whpping out a plug to just check it. If they look dirty clean them up, and refit.

 

[Silky-S3]

Did you fit HPFP in a clean environment (as much as possible in real world), and then use the recommended lube to bed it in?

Might be worth whpping out a plug to just check it. If they look dirty clean them up, and refit.

Yep, it was spotless (I’ve got a engineering workshop which has clean room), and used plenty of lube to bed in. Are you thinking it could be the FP? I'll check the plugs, FP/CF, and intake hose this weekend and report back...

 

[essIII]

I'm currently having what sounds like an identical issue - car's done 75k and is on standard fuel pump internals. Cam follower changed at 60k. From a few other posts I've read it sounded like it could be a failing PCV - I'm fitting a catch can at the weekend and am hoping that resolves it. May be a red herring but just throwing it out there.....

 

[Silky-S3]

I'm currently having what sounds like an identical issue - car's done 75k and is on standard fuel pump internals. Cam follower changed at 60k. From a few other posts I've read it sounded like it could be a failing PCV - I'm fitting a catch can at the weekend and am hoping that resolves it. May be a red herring but just throwing it out there.....

Thats what I'm thinking too mate, air or vacum leak. I dont see how it could be the FP. Let me know how you get on with the catch can.

Thanks

 

[warren_S5]

Be very careful when doing up the bolts which hold on the plate which attaches to the head (for the catch can). I remember reading someone overtightened them and stripped the insides out of the aperture. Cost a lot to put right. Not much beyond hand tight. Be interested to see if this cures it as it's not the greatest part but I'd expect it to outlast 10k!

 

[Silky-S3]

Well, I've just:

Checked cam follower and fuel pump, all fine
Checked and tightened all hose clamps on CAI, all fine, 1 or 2 a little lose
Cleaned MAF, all fine, however the bottom bolt was loose,

and Its cured! Very strange....

 

[Silky-S3]

O, and I topped it up with oil to the Max mark...

Was gonna check plugs as well, but it was fixed before I got to them.

 

[L1ARR]

Glad you sorted out the problem Silky.

 

[warren_S5]

Glad you sorted out the problem Silky.

+1

 

[Silky-S3]

Cheers guys. Can move on to next mod now!

 

[essIII]

Ended up tiling a bathroom floor instead of fitting the catch can this weekend. Will update the thread when I eventually get round to fitting it to let you know if it resolved my erratic idle.

 

[essIII]

Be very careful when doing up the bolts which hold on the plate which attaches to the head (for the catch can). I remember reading someone overtightened them and stripped the insides out of the aperture. Cost a lot to put right. Not much beyond hand tight. Be interested to see if this cures it as it's not the greatest part but I'd expect it to outlast 10k!

Cheers for the tip on bolt tightness - short story is that the installation of the catch can seems to have resolved my idle issues - revs fall back to about 800 rpm rather than clinging on to 1500.

 

[warren_S5]

Cheers for the tip on bolt tightness - short story is that the installation of the catch can seems to have resolved my idle issues - revs fall back to about 800 rpm rather than clinging on to 1500.

Nice one mate, pleased for you. Know how you must have felt as mine was doing my head in on the 8P2!

 

[Silky-S3]

Glad you got sorted mate. Might fit a catch can at some point.