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Thread: Rough idle

  1. #1
    Registered User Brav's Avatar
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    Rough idle

    Sad, I was just commenting how reliable my car has generally been aside from problems that I instigated w mods. I was driving in town after I had got on it hard on the freeway and all of a sudden the throttle was behaving erradically. When I would let off it would maintain speed. Then as I come to a stop it sounded like it would die. If I gave it gas it would respond well and seem to smooth out. But rpms were holding after I let off. Also brakes went hard and nearly non functional as I came to a stop. I won't have access to a vag com till later. CEL was already on. For post catalyst. Generic scanner found no other faults. Video uploading now.

    Seem like vacuum leak or electronic? Seems to still boost.

    http://www.youtube.com/watch?v=2FRFmQcg-v8

    http://www.youtube.com/watch?v=ftq1VhrDKEM
    Last edited by Brav; February 18th, 2012 at 20:40.
    03 RS6 | Daytona Gray on black | KW V3 | Rotiform 19x10 Wheels | REVO ECU | MTM TCU | 170k miles and counting..
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  2. #2
    Registered User Bigglezworth's Avatar
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    Rough idle leading to stall and no poweer assist for brakes has always been a tell tale sign of a vaccum leak in my experience.
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    Registered User ben916's Avatar
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    Quote Originally Posted by Brav View Post
    Sad, I was just commenting how reliable my car has generally been aside from problems that I instigated w mods. I was driving in town after I had got on it hard on the freeway and all of a sudden the throttle was behaving erradically. When I would let off it would maintain speed. Then as I come to a stop it sounded like it would die. If I gave it gas it would respond well and seem to smooth out. But rpms were holding after I let off. Also brakes went hard and nearly non functional as I came to a stop. I won't have access to a vag com till later. CEL was already on. For post catalyst. Generic scanner found no other faults. Video uploading now.

    Seem like vacuum leak or electronic? Seems to still boost.
    I think you are on the right track with the vacuum leak - that was a telltail sign with John's but his was at freeway speed and pucker factor...
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  4. #4
    Registered User Brav's Avatar
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    Good, confirming my suspicions. Honestly it may be a blessing in disguise. At least I know what to hunt for. And may be the source of my not so smooth power. And other random yet not so significant codes. Although I had a leak test done with a fog machine last month and just showed small leak from IC. Maybe maf seals? I just had new ones put in.
    03 RS6 | Daytona Gray on black | KW V3 | Rotiform 19x10 Wheels | REVO ECU | MTM TCU | 170k miles and counting..
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  5. #5
    Registered User ben916's Avatar
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    the easiest think to check/change would the be MAF seals FIRST and then perhaps listen for a leak...
    John's vacuum leak was under the intake manifold....
    SOLD - 03 RS6 Avus (905355)
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  6. #6
    Registered User Brav's Avatar
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    I inspected them myself when Raven had the box off. Looked good.. I doubt the installed wrong. Maybe. Will inspect and report back
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  7. #7
    Registered User ben916's Avatar
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    Also your MAF cables might be frayed?
    SOLD - 03 RS6 Avus (905355)
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  8. #8
    Registered User kday's Avatar
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    A leak that causes you to lose power brakes (a vacuum leak proper) will be something after the throttle -- so MAFs, intercoolers, etc. don't apply.

    Unfortunately this car has a boost sensor (mounted before the throttle), not a MAP sensor, so you can't use VAG-COM to measure vacuum. You could tee a mechanical gauge into a line somewhere I guess.

  9. #9
    Registered User Brav's Avatar
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    Thanks for the info kday. generic scanner now shows missfires on every cylinder. So for sure it has to be vacuum.. at idle, after warm, it will hunt now up to 2100-2500 RPM and hang for a while smoothly, then go down to a lumpy dirty idle. then repeat.. over and over.

    I should also note.. this is the first time I have EVER heard the fan stay on after I shut the car off.. WTF. And the air was pretty cold that it was blowing...
    Last edited by Brav; February 19th, 2012 at 01:22.
    03 RS6 | Daytona Gray on black | KW V3 | Rotiform 19x10 Wheels | REVO ECU | MTM TCU | 170k miles and counting..
    "Some people play hard to get... I play hard to want."

  10. #10
    Registered User SzymekCRX's Avatar
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    It's helpful to use a spray to find a vacuum leak

  11. #11
    Registered User ttboost's Avatar
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    Yeah, this car is a PITA with all the lines and hoses. Everytime I have my airbox off, I do a lap around checking for dry rotted hoses, adding zipties, using a sledge hammer on the back on my airbox when I put it back on...etc...
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    Brav, just watched your youtube video....I got a case of beer that says it is one of your MAF sensors and/or associated wiring). Mine did the exact same thing and I spent a month chasing my tail looking for vacuum leaks and replacing MAF seals. I finally bought an OBD-II to USB cable on eBay for a couple of bucks and downloaded the VCDS-Lite software. Spent 4 hours to get it to work on my computer but had my answer 10 minutes after I plugged it into the car. Mine showed G70 MAF reading about 5 and G246 MAF reading about 0.3. Swapped the MAF's to confirm it wasn't wiring and to figure out which one was G70 and G246 (left/right). Replaced it and it has idle like a champ ever since.

    For some reason because we have 2 MAF's the ECU won't throw a code if one is toast. Best way to trouble shoot (and in my opinion leave it) is to take the MAF's off the airbox and put them in the intake. It'll save you from having to use a hammer to put the airbox on and possibly skank a seal (which I've done) and it will save what is left of your MAF wiring (keeps it from being twisted every time you take the box off).

    I don't know why your brakes quit, but I'd bet unrelated (maybe the engine quit?)

    Good luck!
    Last edited by 905084; February 19th, 2012 at 14:50.

  13. #13
    Registered User Brav's Avatar
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    Thanks for the input. I have brand need MAFs so I hope one is not bad. I used my Torque generic scanner and both MAFs seemed to dead normal. At cruise they were jumping around. Brakes were out as I limped it home most of the way. It seemed to come back after a period of decelerstion, maybe built you vacuum. I searched all last night for a vac diagram. Only found SAI and pcv routes. Anyone got a full diagram?

    Another note - whike looking around under the good with engine running, I could hear a very loud hollow sucking sound. Today I will pull the airbox and have a look and VAG it.
    03 RS6 | Daytona Gray on black | KW V3 | Rotiform 19x10 Wheels | REVO ECU | MTM TCU | 170k miles and counting..
    "Some people play hard to get... I play hard to want."

  14. #14
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    I hear that loud sucking sound every time I start my RS, seems to be coming from my wallet area Good luck, sounds like vacuum then. Any rich/lean bank codes?

  15. #15
    Registered User Brav's Avatar
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    LOL ya maybe here was it. Yes I had misfire on all cylinders and correction limit exceeded for lean condition.
    03 RS6 | Daytona Gray on black | KW V3 | Rotiform 19x10 Wheels | REVO ECU | MTM TCU | 170k miles and counting..
    "Some people play hard to get... I play hard to want."

  16. #16
    Registered User Brav's Avatar
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    Finally got a VAG COM... heeear we go! 19 Faults in one group, new personal record

    VIN: WUAPV64B03N905315
    -------------------------------------------------------------------------------
    Address 01: Engine Labels: 077-907-558-BCY.lbl
    Part No: 4D1 907 558 D
    Component: 4.2l V8/5VT G 0003
    Coding: 0006752
    Shop #: WSC 13876 409 403238
    VCID: 2F67E54FBD066C1

    19 Faults Found:
    16487 - Mass Air Flow Sensor (G70)
    P0103 - 001 - Signal too High - Intermittent
    17482 - Mass Air Flow Sensor 2 (G246)
    P1074 - 001 - Signal too High - Intermittent
    18393 - Coolant Control Module 2 (J671)
    P1985 - 002 - Malfunction - Intermittent
    17585 - Bank2: O2 (Lambda) Correction Behind Catalyst
    P1177 - 001 - Control Limit Reached - MIL ON
    17887 - Brake Boost Vacuum System
    P1479 - 008 - Mechanical Failure - Intermittent

    16684 - Random/Multiple Cylinder Misfire Detected
    P0300 - 001 - - MIL ON
    16688 - Cylinder 4
    P0304 - 001 - Misfire Detected - MIL ON
    16692 - Cylinder 8
    P0308 - 001 - Misfire Detected - MIL ON
    16690 - Cylinder 6
    P0306 - 001 - Misfire Detected - MIL ON
    16687 - Cylinder 3
    P0303 - 001 - Misfire Detected - MIL ON
    16686 - Cylinder 2
    P0302 - 001 - Misfire Detected - MIL ON
    17536 - Fuel Trim; Bank 1 (Mult)
    P1128 - 001 - System too Lean - MIL ON
    17538 - Fuel Trim; Bank 2 (Mult)
    P1130 - 001 - System too Lean - MIL ON
    17544 - Fuel Trim: Bank 1 (Add)
    P1136 - 001 - System too Lean
    17546 - Fuel Trim: Bank 2 (Add)
    P1138 - 001 - System too Lean
    16891 - Idle Control System RPM
    P0507 - 001 - Higher than Expected. - Intermittent - MIL ON
    16685 - Cylinder 1
    P0301 - 001 - Misfire Detected - MIL ON
    16689 - Cylinder 5
    P0305 - 001 - Misfire Detected - MIL ON
    16691 - Cylinder 7
    P0307 - 008 - Misfire Detected
    Readiness: 0000 0000

    -------------------------------------------------------------------------------
    Address 03: ABS Brakes Labels: 4B0-614-517.lbl
    Part No: 4B0 614 517 AD
    Component: ESP 5.7 RS 6 2310
    Coding: 06697
    Shop #: WSC 02195
    VCID: 63CF597FF14E981

    2 Faults Found:
    01119 - Gear Recognition Signal
    35-10 - - - Intermittent
    18265 - Load Signal
    P1857 - 35-10 - Error Message from ECU - Intermittent
    03 RS6 | Daytona Gray on black | KW V3 | Rotiform 19x10 Wheels | REVO ECU | MTM TCU | 170k miles and counting..
    "Some people play hard to get... I play hard to want."

  17. #17
    Registered User kday's Avatar
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    Codes for "too lean" seem consistent with a vacuum leak, and being too lean could cause misfires. Same with idle higher than expected, a sucking sound, and of course the lack of brake boost. That's a lot of signs pointing to a plain old vacuum leak. Seems like it must be a pretty big one; hopefully that means it will be easy to track down. Not sure how the MAF codes fit in.

  18. #18
    Registered User Brav's Avatar
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    I really hope its something on top of the manifold.. is there much under the airbox that could go wrong? the SAI pump looks fine.
    03 RS6 | Daytona Gray on black | KW V3 | Rotiform 19x10 Wheels | REVO ECU | MTM TCU | 170k miles and counting..
    "Some people play hard to get... I play hard to want."

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