spoon2000

My 2000 A6 4.2 often has a terrible time starting first thing in the morning (but only then). The problem is worst when the temperature is 50 degrees or below. In the first few seconds the motor is running, it surges, then the RPMs drop to almost nothing, then it surges again, followed by drop, etc. Each surge and drop cycle takes about 2 seconds. The cycle repeats 4 or 5 times, after which time the RPMs smooth out and the car drives fine. Lately, the problem has gotten so that when the RPMs drop, the car sometimes stalls.

Any ideas what's causing this?

Thanks very much!

4Driver4

Pull codes, post codes. If no codes, start by replacing the coolant temp sensor.

spoon2000

Thank you, 4Driver4. No current or pending OBD codes. VCDS codes follow.

What made you suggest the coolant temp sensor? How tough is it to swap that out?


Wednesday,12,May,2010,15:04:14:27586
VCDS Version: Release 908.2
Data version: 20100326



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--------------------------------------------------------------------------------


Chassis Type: 4B - Audi A6 C5
Scan: 01 02 03 06 08 15 16 17 18 34 35 36 37 45 55 56 57 65 67 75
76 77

-------------------------------------------------------------------------------
Address 01: Engine Labels: None
Part No: 4D0 907 558 S
Component: 4.2L V8/5V G 0008
Coding: 06752
Shop #: WSC 02325

3 Faults Found:
17704 - Error in Mapped Cooling System (check Temp-Sensor and Thermostat)
P1296 - 35-10 - - - Intermittent
17539 - Oxygen (Lambda) Sensor; B2 S1: Internal Resistance too High
P1131 - 35-10 - - - Intermittent
17549 - Load Calculation Cross Check: Implausible Value
P1141 - 35-10 - - - Intermittent
Readiness: 0000 0000

-------------------------------------------------------------------------------
Address 02: Auto Trans Labels: 01L-927-156.lbl
Part No: 4B0 927 156 BS
Component: AG5 01L 4.2l5V USA 1414
Coding: 00002
Shop #: WSC 02325

No fault code found.

-------------------------------------------------------------------------------
Address 03: ABS Brakes Labels: 8D0-907-389.lbl
Part No: 8D0 907 389 E
Component: ABS/ESP allrad D36
Coding: 06397
Shop #: WSC 09416

No fault code found.

-------------------------------------------------------------------------------
Address 08: Auto HVAC Labels: 4B0-820-043-MY1.lbl
Part No: 4B0 820 043 L
Component: A6-Klimavollautomat D64
Coding: 00180
Shop #: WSC 02325

No fault code found.

-------------------------------------------------------------------------------
Address 15: Airbags Labels: 4B0-959-655-AI8.lbl
Part No: 4B0 959 655 F
Component: Airbag Front+Kopf 1002
Coding: 00304
Shop #: WSC 00000

No fault code found.

-------------------------------------------------------------------------------
Address 16: Steering wheel Labels: 4B0-907-487.lbl
Part No: 4B0 907 487 D
Component: Lenkradelektronik D01
Coding: 00103
Shop #: WSC 65535

No fault code found.

-------------------------------------------------------------------------------
Address 17: Instruments Labels: 4B0-920-xxx-17.lbl
Part No: 4B0 920 980 M
Component: C5-KOMBIINSTR. VDO D11
Coding: 03283
Shop #: WSC 00000

No fault code found.

-------------------------------------------------------------------------------
Address 35: Centr. Locks Labels: 4B0-962-258.lbl
Part No: 4B0 962 258 J
Component: Central Lock/Alarm D33
Coding: 15945
Shop #: WSC 02325

1 Fault Found:
01370 - Alarm triggered by Interior Monitoring
35-00 - -

-------------------------------------------------------------------------------
Address 36: Seat Mem. Drvr Labels: None
Part No: 4B0 959 760 A
Component: Sitzmemory D05

No fault code found.

-------------------------------------------------------------------------------
Address 45: Inter. Monitor Labels: None
Part No: 4B0 951 178 A
Component: Innenraumueberw. D04
Coding: 00101
Shop #: WSC 02325

No fault code found.

-------------------------------------------------------------------------------
Address 55: Xenon Range Labels: 4B0-907-357-DYN.lbl
Part No: 4B0 907 357 C
Component: dynamische LWR D03
Coding: 00020
Shop #: WSC 02325

No fault code found.

-------------------------------------------------------------------------------
Address 56: Radio Labels: 8D0-035-1xx-56.lbl
Part No: 8D0 035 195 A
Component: Radio D00
Coding: 00201
Shop #: WSC 00000

No fault code found.

End ---------------------------------------------------------------------

4Driver4

What about these codes? Looks like a problem with the coolant temp sensor, Bank 2 primary O2 sensor at a minimum.

I suggested the CTS because you stated that the problem is temp related and CTS is a common failure item on other Audi's.

spoon2000

Thanks very much! I'll get a CTS today and see what happens when I put it in.

Any ideas about why this CTS http://shop.advanceautoparts.com/web...971702-P_290_R is half the cost of those sold at the online parts vendors?

And any thoughts on using this O2 sensor http://shop.advanceautoparts.com/web...730541-P_291_R which is substantially less expensive than many of the other ones available?

This http://shop.advanceautoparts.com/web...730598-P_291_R is the OEM replacement version O2 sensor.

Am I correct that a faulty O2 sensor would affect gas mileage?

Edd W

The CTS looks fine but you will need a new retaining circlip and O ring. Look on Ebay for someone selling the kit or aks the seller for all three parts.

I would avoid generic O2 sensors, not work the hassle, this is the one I have fitted and it is fine - http://cgi.ebay.co.uk/ws/eBayISAPI.d...m=400102880683

It looks like it may be the same one you have found - LS6287 v/s 16287 ?

I believe the sensor is the same for the 2.7 as the 4.2 - the only difference may be cable length.

spoon2000

Thanks, Edd -- I will get the CTS and if there's not an O ring in the box, there are Audi and VW dealers just down the street that I'm sure will have it and the retaining clip.

I'll stick with the OEM direct fit O2 sensors. Should I go ahead and do both upstream sensors while I'm at it?

Edd W

No, just replace the one which has failed, B2 primary is on your drivers side - just down from the expansion bottle.

spoon2000

What's the easiest access to it -- from above or from underneath the car?

spoon2000

Got the coolant temperature sensor from Advance Auto Parts for $9.99 -- part number WT5129 and it came with an o ring gasket. Stopped by the Audi dealer to get the C clip and while at the dealer, I asked the parts guy to show me the Audi coolant temperature sensor so I could compare it to the one I bought -- the two sensors looked identical in every way.

There was some confusion in the Advance Auto Parts computer about which part I was getting -- if you plug in the car details and ask it for the coolant temperature sensor, it only shows a more expensive option (Bosch or something). However, if you plug in the Audi part number and ask it to cross reference to what's available, it shows the more expensive option plus the sensor I got.

Nice guy at the Audi parts counter printed out the engine schematic for me showing the sensor location -- looks to be easily accessible on the top of a tube running between the headers.

Will report again when I get the job done. Thanks again to all for the advice.