Refurbishing an AUA

[Graham2704]

I used to have all these problems with my BBY but now it runs brilliantly. Have you checked the Earth wire behind the headlight and I mean take it off completely and check under the sleave mine looked all ok but it was broken in places.


I also took the protective tape off the loom to each coil and followed them all back to the start with 2 of them had exposed wires only a little where the wire started breaking down. I got some heat sleaves and slid them over each wire then shrank them on now runs better. I replaced the Throttle body,EGR, Maf sensor 4 new Genuine injectors trying to chase faults it's cost a small fortune I should have gone with these 2 easy ones to look at first.

Hope this is of some help first before spending money. Graham

 

[Robin_Cox]

Ironically, I did clean the earth last week. Starting is a lot better than it had been for the past month or so without any change in the battery etc. I've gone all in and spent another £1.50 on a new oil lid for the rocker cover - there is something about the quite liquid (ie recent) coating of oily stuff just around the lid that makes me wonder if it is seeping slightly, and as I already have the manifold pressure sensor in the garage (but the lid is quicker to replace due to Amazon overnight delivery) it seemed like a no-brainer. Fingers crossed.

 

[Graham2704]

I did the same thinking a clean should do it but it only worked a bit. I would say take an hour to just double-check strip the loom back to each coil and have a look.

 

[Robin_Cox]

I did the same thinking a clean should do it but it only worked a bit. I would say take an hour to just double-check strip the loom back to each coil and have a look.

There is only the one coil pack on an AUA unlike the BBY - it was new 18 months back along with plugs and leads (all Bosch) - the leads are still supple and showing no signs of wear or dirty contacts. Unlike back then when this thread started though, the impression I have is that this week's problems are entirely related to air leaks impacting on fuel ratio (or a sensor going a bit doolally causing issues with these) - back then there were misfires, knackered EGR, TB & pipes full of tar, worn out injectors and so on resulting from years without maintenance - and error messages related to these. This has happened so suddenly I am wondering whether it has been a mechanic-generated problem (ie what IT folk would refer to as PICNIC - problem in chair, not in computer!) as I took the plugs out a fortnight ago (and I had to remove the oil lid to take the plugs off) ... we'll see.

Thank you for your thoughts and comments though - all grist to the mill and very much appreciated. Even if I don't benefit from them directly on this occasion, someone following in my footsteps may see your suggestions and set themselves on the right path for their own vehicle.

 

[Robin_Cox]

The replacement oil cap arrived overnight - Febi 02113 for £1.20 on Amazon. First thing noticed was that the rubber seal on the back of this lid looked noticeably thicker, and in comparison to the one I was replacing, once fitted, as it engaged to the locked position, there was a much more noticeable click. Also not possible to compress it down further, whereas the one on the car before felt like it could still be depressed slightly when in situ. Car has run better since, although lockdown means that the frequency of use is less than normal so I can't comment as to whether this is the final fix.

 

[Robin_Cox]

So. Back to reality after another 22 months, and over 199k on the odometer now. There's been a sporadic lambda (heater?) earth error message and the manifold barometric pressure sensor implausible (sporadic) message over the year and a bit but nothing consistent - and emissions are fine in MOTs. My other half mentioned at the weekend that there had been another incident of surging / dying revs with various lights coming on while waiting at a junction - but on restarting the car she was able to drive home. 3 more days without issue, then last night (heavy rain) the lights all came on together with sporadic stalls / restarts / surging - in traffic - she got home but wasn't happy. So she has my Tdi until it's resolved.
Starting the car (still warm) with the reader plugged in revealed three stored errors - a lambda one, the barometric pressure sensor implausible one, and an air leak one. The ABS, EPC and EML lights all illuminated and did not go out when errors cleared, even when there are no stored errors in the engine ECU. The engine itself at idle was hunting up and down cyclically over around 1000rpm suggesting a feedback loop on mixture.

I'm guessing now, but is this suggestive of something being up with the front lambda sensor? It was replaced 3 or 4 MOTs ago along with the knackered cat and exhaust (years of poor maintenance had caused a lot of raw fuel to go through the exhaust), but I remember the comment being made that the lambda supplied was a generic so they had to swap the plug over - and I'm wondering if this may also be a contributory factor, possibly to the heater earth sporadic issue.

Secondly many folk here have commented that generic lambdas are a waste of time. I've ordered an NGK LZA11-1 / 1825 as recommended on other threads here as if I'm going to replace it I'd rather it is a proper one.

This morning (car stone cold), I put the reader in and started up. EPC still on, but no engine light or ABS. Errors stored 2 - "check DTC memory of a/c" (which I can't do on the reader as it doesn't speak to Climatronic) - and barometric pressure sensor implausible, sporadic again. Idle completely smooth as normal, so the only apparently unusual thing is the EPC light being on.

So it appears that the issue is maybe linked to the engine being up to (full?) temperature, and possibly an air leak / barometric sensor / lambda issue causing erratic mixture issues.

Any thoughts appreciated. I simply don't have time to look at the engine during daylight until the weekend in case of anything else obvious like the oil cap being loose or a cracked pipe, so it's back to cycle commuting again ..

 

[Robin_Cox]

Starting the car (still warm) with the reader plugged in revealed three stored errors - a lambda one, the barometric pressure sensor implausible one, and an air leak one. The ABS, EPC and EML lights all illuminated and did not go out when errors cleared, even when there are no stored errors in the engine ECU. The engine itself at idle was hunting up and down cyclically over around 1000rpm suggesting a feedback loop on mixture.

I'm guessing now, but is this suggestive of something being up with the front lambda sensor? It was replaced 3 or 4 MOTs ago along with the knackered cat and exhaust (years of poor maintenance had caused a lot of raw fuel to go through the exhaust), but I remember the comment being made that the lambda supplied was a generic so they had to swap the plug over - and I'm wondering if this may also be a contributory factor, possibly to the heater earth sporadic issue.

Secondly many folk here have commented that generic lambdas are a waste of time. I've ordered an NGK LZA11-1 / 1825 as recommended on other threads here as if I'm going to replace it I'd rather it is a proper one.

I thought that this thread was up to date, but it's about 11 months out and missing some new info.

The generic lambda fitted in 2019 was replaced with the genuine NTK one that I mentioned buying above (in November 2022) some time in mid December 2022. Completely revelatory. Overnight improvement in fuel economy that has been sustained over the past year - even my other half can get to 250 miles on a 34 litre tank in ordinary short-hop commuting, and over a 2-3 week spell using this car instead of my BHC, including commuting and a drive up the A90 to visit @George Hogg in June I averaged high 40s mpg across the tank by fuelly. Looking at the fuelly logs over the past year and a half, fuel economy before replacement was around 34mpg, and subsequently around 38.5. Fillups now ~nearly 3 weeks apart instead of regular fortnightly.

It just goes to show over the 5 years we've had the car that nothing beats proper maintenance. Improving the consistency of the spark (coil, cables, plugs), airway and integrity of airway (TB, EGR, catch can, oil cap), and fuelling ratio (injectors and lambda) result in the engine running properly!

 

[Robin_Cox]

Spring 2024, an update, and at the end a technical question for the floor.

Over winter I noted that the occasional "all lights on the dash and loss of throttle body control" incident described above would happen on a properly cold morning after starting up that seemed to tally with hypothesized low voltage, possibly indicative that the 90A alternator on the AUA isn't now churning out enough sparks to keep the battery fully charged in winter with daily short commutes. I have a 110A alternator from an FSi ready to go for refurb at a place recommended by @depronman to replace this with some time this spring. So in addition to the 60W incandescent lightbulbs keeping the windows thawed overnight I've had the CTEK permanently in the car giving a battery top up every few nights, with the result that starting the car is always instant and there hasn't been a single warning light panic all winter. Without CTEK, voltage (without load) around 13.2-13.5 with engine/alternator running which is a bit off the 14.something I see in my Tdis with refurbed 140A alternators.

Most days I go out and idle the car for enough time without load (3-5 minutes) for the engine to settle down to a steady idle around 900-950rpm while getting the windows cleared - still not fully warmed up, but not stone cold "choke fully out" fuelling that can cause the car to be a bit all-or-nothing low down for the first minute's driving (which my other half doesn't like on her commute!).

Couple of times recently in the minute before switching off (coolant temp approaching 50˚C according to reader), I'd noticed the idle becoming very slightly lumpy but nothing special. Yesterday this went a step further - flashing engine light came on and the idle went distinctly 3-cylindered. Reader said that cylinder 1 was misfiring. Reset the error code and restarted with the misfire readings page open. Smooth to begin with but with cylinder 1 (only)'s misfire count running like a stopwatch right from startup until it hit the cut-off count and switched to 3 cylinders again. Reset, switched off, switched on. Cylinder 1 misfire count running - whereupon after a couple of seconds I increased the revs to 1500 or so - the faint trembling stopped, and the #1 misfire count stopped, zeroed itself after a few seconds and never came back.

So. Intermittent cylinder 1 misfire, only after the engine has partially warmed up, only on the idle and goes away providing there are some revs.

Earth of some description - perhaps related to cylinder 1 itself or its injector? Crankshaft sensor relating to misfire count messing things up? Any thoughts?

I've not yet had the bonnet off to check the spark plug cords for any damage; as described in thread above, plugs, cords, coil, injectors, lambda, kitchen sink all replaced over the course of the last 4 years / 20,000 miles with quality parts and are generally in good nick as far as I can tell, which is why I'm thinking about things I haven't touched so far. Starter earthing point was cleaned a couple of years ago, and the starting is itself fine.

 

[Deleted member 20348]

Hi,
The AUA and BBY engine is straight forwards to work on.
If you have a spring clamp tool, small socket set, trim tool removal kit and some torx and hex bits and a ratchet your all set.

Before starting on the fuel system I would replace the rubber seals and metal gaskets on the engine.

If we decouple each factor of engine combustion we get something like

• Air
• Fuel
• Spark
• ECU
• Sensors & components

The combustion efficiency (miss fire) error code can be difficult to track down so I tend to ignore it until I've done a little house keeping.

Anything VCDS is telling me at this point I take with a pinch of salt until I know all the seals are freshly replacef.
NOTE
Don't stop give up until all the items are renewed, it's worth the effort to get right.

Work as spotlessly clean as your environment will allow (I work outside) and it's important to clean each part before refitting. Please check for cracks in plastic and worn/split hoses. If in doubt fix it or bin it and buy new.

The throttle body junction​

Under the throttle body there are 4 airways connected to the lower alloy mounting. So we have 4 chances that unmetered can enter after the metered throttle body.

I would start there and radiate out replacing gaskets and hoses.

Also relevant to your miss fire is the inlet manifold and its x4 seals to the cylinder head and the x8 injector seals.

To make working in the engine bay easier, it's not necessary but I suggest removing the wiper arm, plastic scuttle and cabin heater fresh air intake.

The other items with rubber parts are in the following photos.

Good luck!









I'm not a mechanic. Sharing ideas and brief overview followed by the no cost/ low cost way of work is the aim.