Trying to find cause of TFSI Avant occasional stutter - any ideas

[IanMcD]

Hi guys
Having had to sell my much loved B5 2.8 Quattro Avant after 20 years due to the London ULEZ, I liked the look of the B7 and dived in with a BUL engined S-line Special Edition Quattro Avant (it even has the DTM wheels).

Its a great car so see why there is so much affection for these on this forum.

Want to keep it for a while so have been through the checks and replacements that are advised.

The one thing I haven't been able to fix though is an occasional stutter. If anyone has advice on what to look at next it would be really helpful

Car starts fine and ok while warming up. Once it gets near to fully warmed there will be an occasional stumble at idle.Sometimes it catches it, sometimes the engine cuts out. It will immediately restart. Very occasionally when driving at speed it might stutter for a moment and then ok (stutter feels like it is pulling back for a moment)

Things already done over the last 2 years - as not done by previous owner and car has done 90K miles
- Checked HPFP cam folder (First garage I had do work on it broke a HPFP fixing while checking the cam follower and had to replace the HPFP with a non VAG one)
- Replaced cam belt
- Replaced the cam chain and tensioner
- Replaced thermostat and temp sender (temp wast getting to 90)
- Replaced the fuel filer
- Replaced the N75 valve
- Have fitted a VIS balance shaft delete freewheel (car was making some occasional strange vibrations so was worried it could be that) - now runs very smoothly
- While oil pan was off also had oil pick-up changed
- Head carbon cleaned
- Diverter valve replaced

Garages I have taken it to haven't found any error codes that help (and this included a VAG specialist).

Any pointers on what to do next would be great

Thanks

 

[northpole]

I'd start with running a fuel system cleaner, regardless if you run premium fuel, the goal is to give the injectors a cleanout, but more likely, it could be a coilpack that is acting up.. they don't last forever, and make sure the sparkplugs are all the same brand and gapped properly. I don't see any other reason for it to trip over itself like that, especially if it doesn't leave a faultcode in the ecu... it could be sensor related though but that would leave a faultcode... if either camposition sensor or camshaft sensor have an intermittent fault, the engine can just cutout at any given time... so if you haven't scanned the car yet, i would start with that, just to make sure the sensors are fine, if hey are than it can be one of the other causes I pointed out.

I'm sure someone else will tell you whatever i missed or point you to something completely different.

 

[Charlie Farley]

Hi guys
Having had to sell my much loved B5 2.8 Quattro Avant after 20 years due to the London ULEZ, I liked the look of the B7 and dived in with a BUL engined S-line Special Edition Quattro Avant (it even has the DTM wheels).

Its a great car so see why there is so much affection for these on this forum.

Want to keep it for a while so have been through the checks and replacements that are advised.

The one thing I haven't been able to fix though is an occasional stutter. If anyone has advice on what to look at next it would be really helpful

Car starts fine and ok while warming up. Once it gets near to fully warmed there will be an occasional stumble at idle.Sometimes it catches it, sometimes the engine cuts out. It will immediately restart. Very occasionally when driving at speed it might stutter for a moment and then ok (stutter feels like it is pulling back for a moment)

Things already done over the last 2 years - as not done by previous owner and car has done 90K miles
- Checked HPFP cam folder (First garage I had do work on it broke a HPFP fixing while checking the cam follower and had to replace the HPFP with a non VAG one)
- Replaced cam belt
- Replaced the cam chain and tensioner
- Replaced thermostat and temp sender (temp wast getting to 90)
- Replaced the fuel filer
- Replaced the N75 valve
- Have fitted a VIS balance shaft delete freewheel (car was making some occasional strange vibrations so was worried it could be that) - now runs very smoothly
- While oil pan was off also had oil pick-up changed
- Head carbon cleaned
- Diverter valve replaced

Garages I have taken it to haven't found any error codes that help (and this included a VAG specialist).

Any pointers on what to do next would be great

Thanks

Welcome on board, chap. It's always nice to see new B7 owners join the forum.
And may I say you made a perfect choice , having been a B7 owner myself for over 11 years until a few months ago, B7 ownership, whichever variant, does have its ups and downs which you may have already realised...lol
You will find like-minded B7 owners here always happy to share knowledge and insight so just ask.
I recently let my B7 special edition go after 11 years, and massive outlays and regretted it soon afterwards, but hey that's life.

Having noted what has been done to the car , may I ask, was this all work you carried out or previous owners?
If it was you, did the problem start after any specific work or just without any obvious cause? The reason I asked is that sometimes one fix can just be the catalyst for other issues that may have been there for a while, just waiting to rear their heads.

What I would suggest before rushing into any more parts etc, is to run vcds and do some real-time logs etc and see what more specific modules are showing, such as requested and actual figures for fuel delivery / pressures etc , also on the igintion etc to get a better understanding on how the engine is running at given points inc idle speed .

The thing with fault codes is that they only tend to ping up when a specific problem occurs or the part or circuit is out of the specified range, so you could in fact have a very subtle problem but it is not out of spec enough to generate a fault but you may still experience random issues.

I wont go over the items it could be as that would just be a route to endless possible sources of failure , it is very easy to just keep throwing money, time and parts at aproblem which may in fact be something very simple to recitfy with the use of some good diagnostics and work through whats working to spec or not.

It could be something as simple a coil pack or a relay , the latter can cause very subtle erratic running, random injector problems at that milage are very common even if they have been cleaned, like I say , it could be one of a multitude of possible causes, hence the vcds route.

let me know how you get on as i may be able to assist you further.

 

[IanMcD]

Hi guys.
Wow. Thanks for getting back so quick. A few things there to look at so will start with some real time logs and go from there.
Keeping these older Audis going only really works through sharing/suport on these type of forums so appreciate the help.
Have a fun week

 

[northpole]

it's more the fact that previous owners didn't do the maintenace in time because they rather sell the car off and get another one... people like us try to keep them going.

 

[Bradderz_1988]

Symptoms your describing sound exactly like when my crank sensor was failing and also wouldn’t throw any codes.

Swapped that out and now all ok.

Another symptom I’ve experienced was cutting out and then non start which turned out to be a dying LPFP but would also experience non priming of pump on door opening and also ignition switch on.

 

[IanMcD]

Symptoms your describing sound exactly like when my crank sensor was failing and also wouldn’t throw any codes.

Swapped that out and now all ok.

Another symptom I’ve experienced was cutting out and then non start which turned out to be a dying LPFP but would also experience non priming of pump on door opening and also ignition switch on.

Thanks will look at that as well

 

[Matt275]

Welcome along Ian