2007 Touareg misses/stalls 45 seconds after cold start

[fastguy46]

Straight up, I’m fairly new on this forum. I am the happy owner of a Hex Can II. I’ve been using it to troubleshoot fairly simple things. This one is a bit more subtle. As with my other postings I try to document things well for others who follow.

Car is a 2007 Tourareg with a 3.6L v6. I have had it since 2007. Fairly high mileage, but it’s been very well cared for. I like it and plan to keep it.

First thing in the morning it starts great, tachs up to 1200 rpm as it should. At 45 seconds, as it idles down, the motor has a noticeable miss. If I’m driving it, the motor might stall. Regardless, it starts, idles and runs fine the rest of the day. The problem is only on first start in the morning when it’s cold - about 40 degrees F here. No CEL, pending or otherwise.

Worthy of note, the problem is the same regardless of emission systems being ready or not.

Unrelated, over the past few months I have changed;

• Air filter
• OEM Plugs & Coils
• MAF Sensor - Bosch
• Bank 1 O2 sensors. OEM front, Bosch rear.

I’m thinking fuel delivery, so today I used VCDS to log the rail pressure and RPM on start. We see the miss (~200 rpm drop) , however the fuel pressure is fine 70.11 bar. I will figure out how to link an image if it's important.

Other than bank 2 O2 sensors, I’m out of ideas.

Appreciate the help.

VIN: WVGZE77L37D001532   Mileage: 274940km-170839miles
-------------------------------------------------------------------------------
Address 01: Engine        Labels: 03H-906-032-BLV.clb
   Part No SW: 03H 906 032 D    HW: Hardware No
   Component: T 3.6-FSI-LEV2  G00 9709
   Revision: --H05---    Serial number: VWZ3Z0F6461149
   Coding: 0001175
   Shop #: WSC 31414 000 00000
   VCID: 2313FF8E07CFD6E2329-5160
   VINID: 9E65EA5471DC0C750000114308AF7C09C4

1 Fault Found:
005241 - Brake Boost Vacuum System
               P1479 - 008 - Mechanical Failure
             Freeze Frame:
                    Fault Status: 01101000
                    Fault Priority: 0
                    Fault Frequency: 6
                    Reset counter: 255
                    Mileage: 274863 km
                    Time Indication: 0

             Freeze Frame:
                    RPM: 988 /min
                    Load: 42.7 %
                    Speed: 2.0 km/h
                    Temperature: 89.0°C
                    Temperature: 30.0°C
                    Absolute Pres.: 980.0 mbar
                    Voltage: 14.097 V

Readiness: 0000 0000

-------------------------------------------------------------------------------
Address 02: Auto Trans        Labels: 09D-927-750.clb
   Part No: 09D 927 750 CP
   Component: AL 750 6A           0901
   Coding: 0004216
   Shop #: WSC 31414 000 00000
   VCID: 7EA5EEFACCED5B0A7D7-5160

No fault code found.

-------------------------------------------------------------------------------
Address 03: ABS Brakes        Labels: 7L0-907-379-MK25.lbl
   Part No: 7L0 907 379 G
   Component: ESP ALLRAD MK25     0203
   Coding: 0014338
   Shop #: WSC 31414 000 00000
   VCID: 3D2729F6816B801224D-5160

No fault code found.

-------------------------------------------------------------------------------
Address 05: Acc/Start Auth.        Labels: None
   Part No SW: 7L0 909 137 A    HW: 5WK 485 02
   Component: G2 Kessy            6700
   Revision: 67005915    Serial number: VWZ3Z0F6461149
   Coding: 0147688
   Shop #: WSC 31414 000 00000
   VCID: 313F05C64D337472B05-5184

   Subsystem 1 - Part No: XXXXXXXXXXX
   Component: ELV                 XXXX

1 Fault Found:
00181 - Access/Start Authorization Antenna (in Rear bumper) (R136)
            011 - Open Circuit

-------------------------------------------------------------------------------
Address 08: Auto HVAC        Labels: 7L6-907-040.clb
   Part No: 7L6 907 040 T
   Component: CLIMAtronic R/L     4222
   Coding: 0020030
   Shop #: WSC 31414 000 00000
   VCID: 41DF5506FD93E4F2405-5184

1 Fault Found:
01592 - Air Quality Sensor (G238)
            014 - Defective

-------------------------------------------------------------------------------
Address 09: Cent. Elect.        Labels:. 7Lx-937-049-V1.clb
   Part No: 7L6 937 049 M
   Component:                     3002
   Coding: 0101599
   Shop #: WSC 26030 444 12125
   VCID: 46D5461AD4BDC3CA757-5160

3 Faults Found:
01494 - Bulb for Parking Lamps; Left (M1)
            007 - Short to Ground - Intermittent
00907 - Intervention load Management
            000 - -
01520 - Rain and Light Recognition Sensor (G397)
            008 - Implausible Signal - Intermittent

-------------------------------------------------------------------------------
Address 15: Airbags        Labels: 3D0-909-601.lbl
   Part No: 3D0 909 601 H
   Component: 05 Airbag 8.4E++H01 0562
   Revision: BB38727     Serial number: 0007721:   
   Coding: 0012341
   Shop #: WSC 31414 000 00000
   VCID: 2809E8A27EE935BA67B-5160

   Subsystem 1 - Part No: 7L0 959 339 C
   Component: BF-Gewichtsens. 006 0008

No fault code found.

-------------------------------------------------------------------------------
Address 16: Steering wheel        Labels: 7L6-953-549.lbl
   Part No: 7L6 953 549 H
   Component: Lenksäulenmodul     3401
   Coding: 0010032
   Shop #: WSC 31414 000 00000
   VCID: 44D15C12E281F1DA6B3-5184

No fault code found.

-------------------------------------------------------------------------------
Address 17: Instruments        Labels: 7L6-920-xxx-7LA.lbl
   Part No: 7L6 920 981 P
   Component: KOMBIINSTRUMENT RB8 3211
   Coding: 0007231
   Shop #: WSC 31414 000 00000
   VCID: 46D5461AD4BDC3CA757-5160

No fault code found.

-------------------------------------------------------------------------------
Address 19: CAN Gateway        Labels: 6N0-909-901-19.clb
   Part No: 6N0 909 901
   Component: Gateway K<>CAN      0101
   Coding: 0000006
   Shop #: WSC 31414 000 00000
   VCID: 70B9C0C286B93D7AFFB-5160

No fault code found.

-------------------------------------------------------------------------------
Address 1C: Position Sensing        Labels: 7L6-919-879.lbl
   Part No: 7L6 919 879 A
   Component: JCI PathPoint       2200
   Shop #: WSC 00000 000 00000
   VCID: 45D74116E9BBC8D27CD-5160

No fault code found.

-------------------------------------------------------------------------------
Address 22: AWD        Labels: None
   Part No: 0AD 927 755 AT
   Component: TRANSFERCASE        0114
   Shop #: WSC 00000 000 00000
   VCID: 0D47B936F14B709274D-5160

2 Faults Found:
02039 - Position Sensor in Transfer Case (G398)
            008 - Implausible Signal - Intermittent
02039 - Position Sensor in Transfer Case (G398)
            008 - Implausible Signal - Intermittent

-------------------------------------------------------------------------------
Address 25: Immobilizer        Labels: None
   Part No SW: 7L0 909 137 A    HW: 5WK 485 02
   Component: G2 Kessy            6700
   Revision: 67005915    Serial number: VWZ3Z0F6461149
   Coding: 0147688
   Shop #: WSC 31414 000 00000
   VCID: 313F05C64D337472B05-5160

   Subsystem 1 - Part No: XXXXXXXXXXX
   Component: ELV                 XXXX
   XXXXXXXXXXX ELV                 XXXX

1 Fault Found:
00181 - Access/Start Authorization Antenna (in Rear bumper) (R136)
            011 - Open Circuit

-------------------------------------------------------------------------------
Address 33: OBD-II        Labels:
   VCID: 55F791561C0B78520CD-5160


-------------------------------------------------------------------------------
Address 36: Seat Mem. Drvr        Labels: None
   Part No: 7L0 959 760
   Component: Sitzverstellung     0703
   Shop #: WSC 00000 000 00000
   VCID: 77ABFBDEE3D76A423E1-5160

No fault code found.

-------------------------------------------------------------------------------
Address 37: Navigation        Labels: 7L6-919-887-DVD.lbl
   Part No: 7L6 919 887 MX
   Component:      Navigation     0049
   Coding: 0000101
   Shop #: WSC 31414 000 00000
   VCID: 2809E8A27EE935BA67B-5160

1 Fault Found:
01042 - Control Module; Not Coded
            000 - -

-------------------------------------------------------------------------------
Address 39: Right Light        Labels: 3D0-909-158.lbl
   Part No: 3D0 909 158
   Component: EVG GDL+AutoLWR(r)  0001
   Coding: 0000002
   Shop #: WSC 31414 000 00000
   VCID: 678BAB9EB377FAC2AE1-5160

No fault code found.

-------------------------------------------------------------------------------
Address 46: Central Conv.        Labels: 7L0-959-933.clb
   Part No: 7L0 959 933 J
   Component:    HSG              5115
   Coding: 0000085
   Shop #: WSC 31414 000 00000
   VCID: 43D35F0EE78FF6E2529-4B1E

   Subsystem 1 - Part No: 7L0 959 701 H
   Component: Tuersteuergeraet FS 0201

   Subsystem 2 - Part No: 7L0 959 702 H
   Component: Tuersteuergeraet BF 0201

   Subsystem 3 - Part No: 7L0 959 703 D
   Component: Tuersteuergeraet HL 0201

   Subsystem 4 - Part No: 7L0 959 704 D
   Component: Tuersteuergeraet HR 0201

No fault code found.

-------------------------------------------------------------------------------
Address 47: Sound System        Labels:
   VCID: 55F791561C0B78520CD-5160
   Note: Excessive Comm Errors


-------------------------------------------------------------------------------
Address 56: Radio        Labels: 7L6-035-186-DVD.lbl
   Part No: 7L6 035 186 EX
   Component:        Radio        0049
   Coding: 0014062
   Shop #: WSC 26071 444 82799
   VCID: 0D47B936F14B709274D-5160

No fault code found.

-------------------------------------------------------------------------------
Address 68: Wiper Electr.        Labels: 7L0-955-119-V2.clb
   Part No: 7L0 955 119 K
   Component: Front Wiper         4027
   Coding: 0000341
   Shop #: WSC 31414 000 376832
   VCID: 3C2124F29A71891A133-5160

   Subsystem 2 - Part No: 1K0 955 559 T  Labels: 1K0-955-559-AF.CLB
   Component: RegenLichtSens 011  1110
   Coding: 00208933
   Shop #: WSC 31414

No fault code found.

-------------------------------------------------------------------------------
Address 6C: Back-up Cam.        Labels: 5N0-907-441.clb
   Part No SW: 7L6 907 441     HW: 7L6 907 441
   Component: J772__Rearview      0051
   Revision: 00H07000    Serial number:    PA8 J620695
   Coding: 0000201
   Shop #: WSC 31414 000 00000
   VCID: 72BDCACA88B50F6A09F-5160

No fault code found.

-------------------------------------------------------------------------------
Address 6E: Ctrl Head Roof        Labels: None
   Part No: 7L6 919 044 T
   Component: DACHDISPLAY         0539
   Revision: 00900539    Serial number: 2009289.07 
   Shop #: WSC 31414 000 00000
   VCID: 48C94822DEA9D5BA87B-5160

No fault code found.

-------------------------------------------------------------------------------
Address 76: Park Assist        Labels: Redir Fail!
   Part No: 7L0 919 283 F
   Component: 0E Einparkhilfe     1107
   Shop #: WSC 00000 000 00000
   VCID: 392F3DE69543BC32085-5160

No fault code found.

 

[Uwe]

My guess: Carbon build up on the intake valves.

-Uwe-

 

[fastguy46]

Interesting.

The cam chains and tensioners were changed by a local dealer several years ago, so valve timing is fine. I haven't thought about the valves themselves. Looking at the most recent plug change, the plugs have more carbon deposits than their predecessors.

Doesn't burn any oil, however I did move off of Chevron Techron to Costco gas when 91 octane hit $7.00 a gallon here - about 2 years ago.

I'm thinking I'll use VCDS to look at air mass flow during cold start. Rolling down the highway air mass flow is running ~26 g/s which is pretty good for a motor with 171k on the clock. Cold start is of course a whole different matter.

Thanks for the pointer.

 

[Uwe]

I did move off of Chevron Techron to Costco gas when 91 octane hit $7.00 a gallon here - about 2 years ago.

Gas doesn't have much effect on this in a direct-injected engine like yours. In older, port-injected engines, the fuel went past the intake valves and thus had the opportunity to "wash" them, but on a direct-injected engine, this simply doesn't happen.

This is an oil company's explanation:

The Truth Behind Carbon Buildup

We all know that gasoline is the fuel that provides power in our cars’ engines. But along the way to the combustion chamber, that gasoline provides the additional benefit of serving as a solvent that cleans the intake port and intake valve.

team.valvolineglobal.com

-Uwe-

 

[fastguy46]

Thanks Uwe! Today's test is very interesting.

After start Mass Air flow is right around 22 g/s at 1160 rpm. As the motor idles down the Mass Airflow drops to 10.89 g/s at 1080rpm - right at that point we get a misfire and the motor stumbles.

After recovering from the stumble the mass air flow stays around 10 and everything is fine. The problem, such as it is, is in the transition from 22 g/s to to 10 g/s.

So the question of the day.

- How does the V6 engine control Mass Air flow at idle such that they can cause a 2:1 drop on cold start?

This is actually fun, and totally impossible to work on without VCDS.

 

[Uwe]

How does the V6 engine control Mass Air flow at idle such that they can cause a 2:1 drop on cold start?

On a naturally aspirated engine, airflow is normally just function of throttle angle and RPM, however if the secondary air injection system pulls through the MAF, then it would contribute to the measure flow.

10 seems a bit high for idle. What is it once the engine is fully warmed up?

-Uwe-

 

[fastguy46]

Thanks Uwe!

Fully warmed up at idle, in park - 680rpm 3.34 g/s.

 

[Uwe]

Fully warmed up at idle, in park - 680rpm 3.34 g/s.

That sounds reasonable.

-Uwe-

 

[fastguy46]

Ok - todays thinking is that the car starts up open loop and when the engine transitions to closed loop is when we get the stumble.

It would be great if I can get a boolean representation of loop status. As you point out here https://www.vwvortex.com/threads/does-vag-com-display-open-closed-loop-status.2168794/ it's not about what VCDS can display, rather about what the ECU can provide.

I'm back to eyeing the bank 2 O2 sensor, which is the one I haven't changed. Maybe it's slow or intermittent.

I only get one shot at this in the morning. Today I'll take a more granular look which cylinders are misfiring and also the O2 sensor voltages.

VCDS sure has made this fun.

 

[Uwe]

It would be great if I can get a boolean representation of loop status.

I don't see that in the native VAG data for this ECU anywhere, but try generic OBD-II, Mode 1, and see if the ECU supports PID 03.

OBD-II PIDs - Wikipedia

en.wikipedia.org

-Uwe-

 

[fastguy46]

Well, determining loop closure turned out to be easier than expected. Both upstream O2 sensors start out at 1.48 volts. Then the left bank closes first and the left upstream O2 sensor drops to 1.21 volts. A short time later the right bank loop closes and the right upstream O2 sensor drops to 1.31 volts. Cascading bank loop closures is something I hadn't considered. All of this happens right around the stall point.

Regrettably (almost) no stumble or miss today. Just a perfectly well behaved motor. Several thoughts here;

1. Measuring O2 sensor voltages has an impact on the motor. Seems like a long shot.
2. Evap Purge came ready today. Evap purge coming ready is a bit unpredictable on my cars. Seems like a long shot too.
3. Posting on other forums indicates instances of such a problem occuring after plugs and coils have been changed. The postings go on to say the problem clears itself after a few weeks. Yet one more long shot.

This has been such a fun problem that I'll be disappointed if it resolves without finding the actual problem.

 

[fastguy46]

We'll the issue documented above has led to a more interesting series of things to think about. Many VW and Audi owners are dealing with similar problems. Likely that Google searches will land here and I want to be clear about how cold start works on 3.6L v6 engines.

VWs and Audis with the 3.6L v6 use something called Homogeneous Split Catalytic Heating during cold start. They inject fuel during the intake stroke as normal and then again on the compression stroke right before the plug fires. Some of us think of this as stratified charge. Misfires are an expected side effect.
This is done to heat the catalytic converters up quickly, which is does. Mine reach almost 800 degrees C in a few seconds.

To be clear, the above process only happens when the engine is stone cold.

I'm working on 2 theories;

1. The rail pressure dips during the 'double tap'. Time to enable Turbo mode and use VCDS to have a look.
2. The fuel injectors spray fine into atmospheric pressure, but struggle injecting into full cylinder compression. Regrettably injectors are really difficult to change on 3.6L v6 engines. Many of the symptoms are consistent with bad fuel injectors.

And here is a question;

• Can VCDS be used to determine when the 'double tap' fuel injection starts, and when it stops? I'm pretty sure the engine miss I am after is on one side or the other.
  

 

[fastguy46]

As it turns out, VCDS is not only a great tool for sorting out problems, but also for creating a mental model of how things work. So by way of VCDS, here is the cold start sequence for VW/Audi 3.6L v6 gasoline engines.

Hit the key and the motor starts;

• The electric secondary air injection pump pushes 26 g/s through the air box at 1200 rpm
• Fuel rail pressure is 70 bar
• Fuel injector duration is 3.5ms

The catalytic converters wake up and start heating up quickly. When they hit 768 degrees C, the motor dials back;

• Mass air flow through the motor drops to 10 g/s
• Fuel rail pressure remains 70 bar
• Fuel injector duration drops to 1.5 ms
• Catalytic converter temperatures are ~500 degrees C

The stall/stumble is right here ^^. While the catalytic converters are hot, the motor is still cold.

When the motor is fully warmed up;

Fuel rail pressure drops to 35 bar
With secondary injection pump off, mass Air Flow drops to 3.57 g/s

Figuring out the stall/stumble should be easy from here.

 

[fastguy46]

Ok, here we go -

• Vehicle stalls shortly after starting on a cold morning;
• Ignition is fine - plugs and coils are new OEM
• Fuel delivery is picture perfect
• Catalytic converters are well behaved and respond quickly
• Car starts and runs perfectly once it’s warmed up.

Bring me a car like that, and my first thought would be MAF sensor. And that’s when the light bulb went on. As indicated at the beginning of this posting, I did replace the OEM factory MAF sensor with the Bosch equivalent. Same Bosch part number minus the VW/Audi logo and part number. Nothing really wrong with the original - just at 171,000 miles I wanted a new MAF sensor.

More importantly I changed MAF sensor over the California summer - 90 degree days and 60 degree nights. No problems at the time.

So the original factory MAF sensor was sitting in the replacement box, surgically clean with the endcaps. Twenty minutes later it’s back in the motor and the stumble/stall problem is completely gone. Six mornings in a row in the low 40s or high 30s.

I see three possibilities;

• The new Bosch MAF sensor is defective.
• The OEM VW MAF sensor is calibrated differently.
• For reasons I can’t begin to imagine, the new MAF sensor needs to be re-learned beyond several months of normal use.

I’ll cap this off with one more really interesting observation;

With the motor completely warmed up, engine off & key on the MAF sensors do show an output and their outputs are different;

• The OEM MAF sensor 1.36 g/s
• The Bosch replacement 1.21 g/s

All puzzles for another day. Hopefully this write up helps others with similar problems. VCDS is a great tool!

 

[Uwe]

I’ll cap this off with one more really interesting observation;

With the motor completely warmed up, engine off & key on the MAF sensors do show an output and their outputs are different;

• The OEM MAF sensor 1.36 g/s
• The Bosch replacement 1.21 g/s

Can you do a full load test on them both, please? With engine fully warmed up, do a full throttle run to the top of second gear at least, and preferably third gear. Obviously log the MAFs while doing this. It would be interesting to see if the Bosch reads lower than OEM across the board.

-Uwe-

 

[fastguy46]

Great idea! The results of the full load test will be interesting.

I'm going to order up the VW/Audi MAF sensor and run the test against that. The local dealer wanted $500 for the factory MAF sensor, which is how we wound up here. I've lost count of how many times similar things have happened with 'OEM' parts.

Like most probems that involve complex embedded software systems, they seem confounding at the time but in the end it all makes sense. The Bosch MAF sensor reports erroneously low mass airflow. The ecu control loop leans out both banks according and the result is a lean stall.

I've also learned a lot of useful things. I wouldn't want to do this for living, but it sure has been fun.

 

[Uwe]

The local dealer wanted $500 for the factory MAF sensor, which is how we wound up here.

Whoa! That's highway robbery. I could understand really high prices if this was a low volume engine like a V10 TDI or a W12 (the latter never came to the USA) but the 3.6 you have was the base engine.

-Uwe-

 

[dieseldub]

What does the fuel trim look like in MVB 32?

The brake booster mechanical failure is an interesting code. A lot of the Touareg VR6s have an absolute pressure sensor in the brake booster pipe near the booster, they also have an auxiliary electric vacuum pump that can come on as-needed.

I see a lot of these where that booster pipe cracks in multiple locations, most commonly right at the barb at the booster itself. That is creating a vacuum leak that can cause misfires and fuel trim codes at idle.

The loss of vacuum at the booster pipe will also cause the ECU to trigger the electric vacuum pump a lot more often than it should normally, eventually can cause it to burn out too from being run too much compared to what it was intended for.

 

[fastguy46]

Thanks All!

The car been running great since the original VW MAF sensor was reinstalled. Back to its snarly self.

Long term fuel trims are interesting.

• Warmed up at idle the long term fuel trims are identical between banks +2.8%. They never change.
• On the highway at 55mph the control loops lean out and diverge a bit. Bank 1 -2.8% Bank 2 -3.9%.

The 'rich at low rpm/load' part would seem to imply vacuum leak. I will definitely check out the fitting at the brake booster. I should fix the mechanical brake booster anyway.

Back to the Bosch MAF sensor. I've rounded up the Bosch technical documents for MAF sensors. Interesting reading.

I want to build a tester for MAF sensors. Static testing is easy. A marine +12v HVAC pump, a couple of lab supplies and an anemometer. MAF sensors also have a response time. Testing MAF response time requires a computer and some simple programming. Work to do here.

Looking at 'less tech savvy' forums, there are certainly undercurrents of MAF sensor swaps solving one problem and creating new problems. I'd really like to get to the bottom of this.

 

[Larry Manton]

1 Fault Found:
005241 - Brake Boost Vacuum System
P1479 - 008 - Mechanical Failure
Freeze Frame:
Fault Status: 01101000
Fault Priority: 0
Fault Frequency: 6
Reset counter: 255
Mileage: 274863 km
Time Indication: 0

I thought this a red flag right out of the Gate. And Possible the two Maf just different enough that one tolerated it a little better than the other.