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New owner, rough idle, black smoke, hesitation - help/ideas needed please!

Discussion in 'Audi S4/A4/A4 Cab (B7 Chassis)' started by margin-walker, Jul 28, 2013.

  1. margin-walker
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    margin-walker Member

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    Hi everyone, I'm hoping to call on your collective experience and expertise. I'm 4 weeks into owning a 2007 A4 TDI 170 s-line quattro special edition. Great car, big improvement on my previous A3 but from day one I've experienced a problem that has yet to be solved.

    Symptoms
    • Rough/lumpy idle (intermittent), jumps between 900 and 1000 rpm
    • Engine shakes when idle is rough
    • Black smoke (excessive) - both on idle and under acceleration, chokes cyclists who get overtaken
    • Hesitation/flat spots - particularly in 3rd gear, at low revs, but car pulls well at high revs to the red line
    • All appear when engine cold or hot
    • No warning lights show (like DPF, check engine)
    • No error codes

    Fixes/inspections so far
    • Audi garage ran diagnostics, no error codes, say nothing wrong with car on a test-drive, confirmed injectors had been replaced under the recall 18 months ago, weren't interested in problems
    • Independent garage run full diagnostics, no error codes, but thought it may be egr cooler. Ran overnight pressure test, said engine/injectors were fine but cleaned manifold out, said it needed a 'good run down the motorway for a few hundred miles (the dealer I bought it from arranged all of this and weren't tech-minded so I'm not sure what 'manifold' he cleaned but he spent a day looking over it, told them if the problem persisted he could do a 'de-coke')
    • I dumped a can of BG244 into a full tank of V-Power to see if it would make any improvement (mpg seems to be better)

    . . . but the symptoms are still there. The dealer I bought it from did go out of their way to help, taking it to Audi and, not satisfied with their explanation, taking it to another independent specialist because they could see the symptoms and thought it wasn't quite right. However, all say there's nothing wrong with the car but I refuse to believe it as extensive google searches bring back lots of cases of similar symptoms but few solutions. The dealer I bought it from were really helpful if severely lacking in mechanical knowledge so wouldn't question any hypothesis thrown at them by a mechanic and aren't very local to me so I'd prefer to arrange any further investigations myself.

    Any ideas, anybody?!

    The other thing I've seen is a few companies doing re-map, DPF delete and EGR delete specifically on the TDI 170. Has anybody had this done and is it a potential solution?

    Thanks in anticipation.
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  2. NHN
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    Boost leak as black smoke is poor combustion.
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  3. margin-walker
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    margin-walker Member

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    Thanks NHN. I guess that could be a simple fix, tricky to find, and something so basic any garage should have considered?! Audi’s attitude of ‘no error codes = nothing wrong’ has been a big disappointment.

    The other thing I’ve noticed, on changing gear it sounds like it’s got a dump valve, venting to atmosphere, is this normal for this engine? I can hear the turbo spool/whistle but my other car was an impreza so I’m used to all of the whistles/whooshes/pops that made but don’t know what is abnormal for the TDI 170 engine.
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  4. markyp2002
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    markyp2002 Member

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    Sounds like your recirculating diverter valve is faulty to me (forgive me if im talking rubbish here, im sure this is the case). I had a similar issues on an old 1.8T Audi A3, changed the diverter valve and that fixed the atmospheric sound, never had any error messages or anything and it didn't seem to effect performance too much in either case!
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  5. MyMateDaveDJ
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    MyMateDaveDJ New Member

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    Im in a similar situation with an A3 iv just brought, same year and engine i believe.
    Idle issues, clear smoke, hesitation and DPF error codes.
    Hope you get it resolved!
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  6. Molnboman
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    Molnboman Active Member

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    Engine shaking at idle?....sounds like your dual mass flywheel may be going "bye bye" too. Does your car vibrate heavily in first and second gear? Tell tale signs that your Flywheel is f@cked Matey. Is there any noise difference when you press the clutch in, when in gear?

    BR
    A
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  7. d4dubs
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    d4dubs New Member

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    Coil pack?
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  8. NHN
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    Its a TDI.
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  9. margin-walker
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    margin-walker Member

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    Hi Molnboman, thanks for your input! There's no vibration/shake when accelerating, it just happens on idle, but it's intermittent. When the idle is steady at just above 900rpm the engine is also steady, no shake, but when the idle decides to jump up and down by 200-500 rpm it's accompanied by the engine shuddering. The engine switches off fine, ie: no shudder.

    The car accelerates well and pulls to the redline, but it has occasional flat spots/hesitation at lower revs, under 3,000 rpm. Somebody has suggested that perhaps the EGR valve isn't closing fully. I'm going to try and get my head under the bonnet when the rain stops and stand there scratching my chin in anticipation of a light-bulb moment.
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  10. margin-walker
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    margin-walker Member

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    Okay, so I took the top engine cover off and had a good look around, tugging/squeezing the hoses, all connections are tight and I can't see any obvious splits/holes in any of them. The only thing I noticed was the plastic air intake which feeds into the airbox wasn't properly sealed where it joins in the middle. See photo, I've outlined in red where it needed pushing together to get a better fit. I'm guessing this won't have much affect.
    air intake thingy.jpg

    I ran the engine for 10 minutes and revved it a few times but couldn't see/hear anything unusual. BUT, when I switched the engine off I could hear what sounded like some servos working away and a slight hissing noise, like air was being expelled for about 6 seconds. Is this usual after switching the engine off?
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  11. margin-walker
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    margin-walker Member

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    Thanks, good luck with yours, it sounds the same only I'm getting no error codes. When I find out what the problem is I'll post the answer on here, hopefully it might help other people with a similar problem.
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  12. gupsterg
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    gupsterg Member

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    The slight hissing noise can be the air con circuit after shutdown ...

    Viewing of measuring blocks using VCDS or dealer VAS diagnostics machine maybe what you require to pin point problem ...

    Perhaps ask for a pressure test to be done on charge air system ...
    Last edited: Aug 6, 2013
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  13. NHN
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    You can actually, on some cars, activate the charge air system with vcds to try & help find leaks.
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  14. gupsterg
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    gupsterg Member

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    NHN I think you referring to the elements which can be tested by doing an output test in module 01? or do you mean it will check the intercoolers and related hoses? as that's what I referring to when stating get a pressure test done ...
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  15. NHN
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    Well there are a few tests, the basic setting in engine is one yes, but also a pressure/smoke tester is also a good one to use, I had the pleasure of using the dealer tool on my car on a weekend, nice piece of kit, no bloody leaks though lol.
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  16. margin-walker
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    margin-walker Member

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    I have a new symptom: starting the car! ​I put the key in the ignition to start the car and it didn't start first time, I had to keep the key turned for a second longer the second time and it started. It's never done this before. Does this provide any more insight?! I'm going to search the forums now. Thanks for all of your help.
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