S3 8l running very rich intermittently - hitting a dead end please help!


Registered User
Hi everyone,

So I am new to owning a S3 8l fantastic car when it works!

Now this is whats happening, I have seemed to get a good grip on the symptoms and believe me this is a interesting one! I will be following this thread to the end posting a cure too, too many threads never conclude!

Stock Engine
Brand new fuel filter
Brand new original MAF
Replaced coolant temp sensor - green cap
Replaced Lambda
Replaced Fuel Pressure regulator
IK22 plugs
Replaced Air temp sensor on plenum
Opened and examined EGR module no loose connections or broken solders.
Wiring checked over cam cover, some splits found and insulated
Any broken connectors like coil packs were replaced
Nothing is really bodged at all
Throttle body was re-adapted (VCDS adaption) checked out OK, just incase it had been fiddled with I ran the adapts
Throttle body has been cleaned

Seems to become more prominent in slow traffic and idle situations recently, almost as if its fouling plugs that bad during low RPM running, it take a good open pedal moment to clear it out and even then it struggles to pick revs smoothly and quickly, whatever is causing this causes the engine to really bog down and is definitely unburnt fuel

I am a test and development engineer so I will be able to support this well, I am just new to the 1.8t

Someone has to have felt this before?

Before I got GT871r I need to resolve this issue

Important but not the cause - I am told the car was flashed, I am working on acquiring some software to read this but I am happy with the MAP, the car ran brilliant when I bought it, it ran even better when I fixed minor leaks on the PCV system.

MAP sensor and Thermostat have not been replaced, this is tomorrows job.

The fault is intermittent, or its there all the time and only more noticeable at certain times.

The fault appears in idle - no load
Cruising low RPM
under boost conditions and also in no boost conditions (idle)

The car runs so rich the plugs become fouled like charcoal, when its in this mode for a few mins and I touch the accelerator the floor is then laiden with a jet stream of carbon from the exhaust, almost as if the fuel is washing the carbon out.

When this fault comes in the car feels surgy and out of power, a definite lack of efficient combustion resulting in what would normally feel like a misfire, you could argue it is a misfire but not the normal coil pack or plug, he fault is definitely in and out, at times the car shifts like a rocket no black smoke at all, at other times I can see the clouds pumping out behind me.

I seem to be able to turn the problem on by blipping the accelerator pedal a few times, on idle the black smoke coming out of the exhaust can be observed as well as black spits of carbon on my hand if I was to briefly put it near the exit flute of the tips.

Vac system has been deleted entirely,

Fuel pressure regulator runs to inlet manifold
Dump valve (Forge) run to manifold
The third larger union on the bottom of the middle of the plenum has been simply blocked.
The head and crank vent to atmosphere

The car ran sweet so I know its a new issue, not one there from previous hands being in it, well not that I have found so far anyway.

On VCDS when I could borrow a set of leads I had no faults, initially I had a few faults due to disconnecting N75 and MAF while running trying to figure it out, ones codes were cleared nothing re appeared, the car was scanned a week later using a snap on modus, no new faults.

Hitting a brick wall here!!

Affects all four plugs, no difference in them they are completely blacked, there is no beige on these what so ever, they look no different to coal. The carbon build up on the tips is ridiculous and the poor MPG speaks for itself,

Something is making my S3 over fuel like crazy and I just can find the fault please help!!




Anyone had a faulty MAP sensor do this?

I don't have a boost gauge on it yet, or anything to monitor the MAP values at the moment so stuck there too...Ross tech is brilliant but pricey, what are my alternative CAN comms options? Ebay VCDS leads? any recommended links?

Thermostat - I have come across some instances on forums of thermostats causing running rich issues, I know the TT allows a check via the AC panel has the S3 got such functionality?

This one s driving round the bend seriously! I am very competent and will be able to support and anwser any questions.

All the sanity checks have been done but ask me your questions give me your thoughts I must get to the bottom of this one!
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Registered User
Hi everyone, I have some ore information to add, this issue appears at any temperature this morning from cold and present all the way until temperature, without VCDS i need to try disconnect things to see if there is a positive or the correct reaction from compoentns, IE disconnectinf MAF makes a diference and so it should as its new, can the same be done with the EGT as a test or will the car defualt out and run max fuel trims

Many thanks in advance



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want to look at fueling with vcds, look at block 001,002,031 - presumes wideband ecu/AMK/BAM engine


Registered User
Thanks a lot!

I have my ross tech cables on there way and should be here by friday so i will do this, what are the nominal values for these blocks at idle?

Im trying to build this picture now so I ca hammer down on the issue as soon as the cables are in.


Site Sponsor
001 you will see lambda adjustment of what its adjusting by as a % to achieve whats asked for in 031
032 is a leaned value and will change as ecu adapts... so if faults cleared(adaptions are reset o zero) it relearns as an "offset"

driving you will look at 001 for live adjustment, 002 to see airflow, 031 to see requested lambda and actual...
<5% is an ok level.... way larger and somethings a miss


Registered User
Thanks badger!

Hoping my leads turn up tommorow, i will take a look at the measurements in these blocks and report ehat i find, in thr mean time i need to keep chasing the wiring as the fault feels on and off, any common wiring problems causing overfuelling or similair you have heard of?

Helps narrow my search


Registered User
Hey Readers, for those following this so far:

VCDS capability as of today, cleared car of all faults to begin with, knowing I had a 200 mile trip ahead I set off and ran a full vehicle scan when I got home here is the log :

I wasn't seeing much going on at block 032, seemed to stay at 0%

The vehicle did start to kangaroo briefly then disappeared, the fault was not there for the whole drive back and just came in briefly this evening, during this time I quickly connected the leads but was not seeing any lamda correction.

I did warn this would be an interesting onw

Anyway I have noticed a Throttle pot fault, this could be suspect if this refers to engine, seems like its actually a fault of the heaters but let me know what you think ! having recently passed an adaptions sequence on the throttle pot im wondering how it could be bad if it fell within the limits during adaptions, have a look at my log and tell me what you think.


VCDS -- Windows Based VAG/VAS Emulator Running on Windows 10 x64
VCDS Version: (x64) HEX-V2 CB: 0.4508.4
Data version: 20190529 DS308.0

VIN: WAUZZZ8LZ11003516 License Plate: KL99APK

Chassis Type: 8L (8L - Audi A3/S3 (1997 > 2005))
Scan: 01 02 03 08 15 16 17 22 35 37 45 55 56 57 75 76

VIN: WAUZZZ8LZ110035169
Address 01: Engine Labels: 06A-906-032-BAM.lbl
Part No: 8N0 906 018 J
Component: 1.8L R4/5VT 0004
Coding: 10710
Shop #: WSC 00000
VCID: 382928C78B41C377329-5160
WAUZZZ8LZ11003516 AUZ7Z0A1839641
No fault code found.
Readiness: 0000 0000
Address 03: ABS Brakes Labels: 8N0-907-379-MK20-E.clb
Part No: 8N0 907 379 E
Component: ESP 20 CAN V005
Coding: 18448
Shop #: WSC 01236
VCID: 3E253EDFA965FD47F85-4B1E
1 Fault Found:
00812 - Brake Pressure Release Solenoid (F84)
35-10 - - - Intermittent
Address 08: Auto HVAC Labels: Redir Fail!
Part No: 8L0 820 043 H
Component: A3 KLIMAAUTOMAT 0105
Coding: 00041
Shop #: WSC 01236
VCID: 2D070993740376DF51F-25A6
3 Faults Found:
00779 - Outside Air Temp Sensor (G17)
30-00 - Open or Short to Plus
00604 - Potentiometer Positioning Motor for Air Flow Flap (G113)
30-10 - Open or Short to Plus - Intermittent
00796 - Fan for Interior Temp Sensor (V42)
41-10 - Blocked or No Voltage - Intermittent
Address 15: Airbags Labels: 8L0-959-655-AI8.lbl
Part No: 8L0 959 655 J
Component: Airbag Front+Seite 5008
Coding: 01104
Shop #: WSC 01236
VCID: 45D75133CCB3AE9FB9F-5184
No fault code found.
Address 17: Instruments Labels: 8L0-920-xxx-17.lbl
Part No: 8L0 920 980 L
Coding: 01444
Shop #: WSC 10001
VCID: 3C2134D7BF79EF57D61-5160
WAUZZZ8LZ11003516 AUZ7Z0A1839641
1 Fault Found:
01176 - Key
07-10 - Signal too Low - Intermittent
Address 22: AWD Labels: 02D-900-554.lbl
Part No: 02D 900 554 B
Component: HALDEX LSC ECC 0006
VCID: 1F1BE35B0EAF944FD33-4B1E
1 Fault Found:
00526 - Brake Light Switch (F)
27-00 - Implausible Signal
Address 35: Centr. Locks Labels:. 8D0-862-257.clb
Part No: 8D0 862 257 E
Component: CV-Pump, Alarm, RC D17
Coding: 15179
Shop #: WSC 00533
VCID: 2F3B139B7E0F04CF633-4F0C
8 Faults Found:
01367 - Central Locking Pump Run Time Exceeded (Likely Leak)
35-00 - -
01371 - Alarm triggered by Door Contact Switch; Driver's Side
35-00 - -
01374 - Alarm triggered by Terminal 15
35-00 - -
01370 - Alarm triggered by Interior Monitoring
35-00 - -
01368 - Alarm triggered by Luggage Compartment Switch
35-00 - -
01365 - Lock/Unlock Switch; Interior
29-00 - Short to Ground
00991 - Interior Lights
28-00 - Short to Plus
00956 - Key 2
09-00 - Adaptation Limit Surpassed
Address 45: Inter. Monitor Labels: 4B0-951-173.lbl
Part No: 4B0 951 173
Component: Innenraumueberw. D03
Coding: 00001
Shop #: WSC 00000
VCID: 6099A0A77351EBB7AA9-4AC2
No fault code found.
Address 55: Headlight Range Labels: 4B0-907-357-AUT.lbl
Part No: 4B0 907 357
Coding: 00014
Shop #: WSC 01236
VCID: 6597B1B36C738E9F59F-51A8
1 Fault Found:
00776 - Level Control System Sensor; Left Front (G78)
31-00 - Open or Short to Ground
Address 56: Radio Labels:
VCID: 55F781733C031E1FC9F-FFFE

End----------(Elapsed Time: 03:09, VBatt start/end: 12.8V/12.7V)-----------
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Registered User
I had a similar problem as you do. It took 2 years to figure it out. I bought a tuned ready car so I had no idea who tuned the car. Some tuners when they remap cars can lock errors (software) so no error is shown and this was done to mine thus the reason why we couldn't find the fault. It ended up to be the EGT sensor. Try to borrow a new one and try.


Registered User
Hey thanks for the reply,

I have still not managed to crack thus one yet, problem seemed to dissapear and alowly re appear,

My next steps wre to flash an original factory map back on to the car and assess the difference,

EGT has popped up in a few searches, seems like gold dust to buy new.