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  1. #1
    Lee Goodall's Avatar
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    Rough idle and slight backfire!!

    Just when I thought it was time for the new turbo...

    My A4 B5 AEB has developed a rough idle problem which after 5-10 secs settles again but the revs do drop very low and the engine has stalled on more than one occasion. After doing certain jobs involving disconnecting the battery the revs are very erratic and the engine much more prone to stalling.

    When I come off of the revs often I get a slight backfire which obviously indicates unused fuel.

    I have recently replaced the MAF sensor and Lambda sensor but this has had no effect on the rough idle although is running much smoother at higher revs.

    Have just given Audi a ring to see how much it'll cost for a diagnostic!?.. 112.00 Got a lead and a copy of VAG-COM from my mate but it says that my car is not OBDII compatible for some reason!!

    Any suggestion or ideas would be appreciated.

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  3. #2
    macca's Avatar
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    not sure about the vagcom code issue, your car maybe not obd2 compatable, but you can still diagnos using vagcom ok.

    have you done a throttle body reallignment? you can do this via vagcom and it shoes you on rosstech's website how to do this.

    also check all your intake hoses for a boost leak, as it sounds that could be a problem. are you still running standard dump valve?
    1998 A4 1.8T Sport - For Saturdays
    2003 VW Golf MKIV R32 - For Sundays
    2000 Peugeot 406 HDi - For when it's raining
    1996 Kawasaki ZX7R - For when I'm late for work!

    Mods- Forge Dump Valve, The Engine Shop Power Plus based Engine (Low Comp. Forged pistons, Arrow H-Section Rods, Newman fast road cams, polished & ported head), 19" wheels, B&M Short Shifter, Greddy Turbo Timer, RS4 Grill, Weitec GTN coilovers, HKS modified air filter, Autobahn88 FMIC, ChippedUK custom map. Some Turbo mods ongoing.

  4. #3
    Lee Goodall's Avatar
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    Confused about the ODBII compatibility as every other 1996 and onwards A4 seems to be fine.. might just be an issue with the lead?

    Not done a throttle body realignment but without the connection to vagcom I'm going to be struggling.

    I was thinking along the lines of a boost leak so I'll investigate.

    I'm running a Forge diverter valve.

  5. #4
    macca's Avatar
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    i think re vagcom, check your cable is right one.

    check for boost leaks and get back.
    1998 A4 1.8T Sport - For Saturdays
    2003 VW Golf MKIV R32 - For Sundays
    2000 Peugeot 406 HDi - For when it's raining
    1996 Kawasaki ZX7R - For when I'm late for work!

    Mods- Forge Dump Valve, The Engine Shop Power Plus based Engine (Low Comp. Forged pistons, Arrow H-Section Rods, Newman fast road cams, polished & ported head), 19" wheels, B&M Short Shifter, Greddy Turbo Timer, RS4 Grill, Weitec GTN coilovers, HKS modified air filter, Autobahn88 FMIC, ChippedUK custom map. Some Turbo mods ongoing.

  6. #5
    mwarrey's Avatar
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    Have you tried cleaning the throttle body ?. I had a rough idle on mine a little while ago. A new set of plugs improved it slightly, so I removed the throttle body and cleaned it with some carb cleaner. This sorted the idle and it is now perfect.

    You can use vag com to do the throttle body alignment afterwards or if you leave ignition on for around 30 mins I have read that it will realigin itself.

  7. #6
    Lee Goodall's Avatar
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    Removed the headlight last night to check for a boost leak around the turbo/hoses area and noticed oil over the turbo to intercooler hose which looked like it had sprayed out of the hose.. hopefully I have found my leak. Going to get the car on stands tonight and have a good look from below.

    If this doesn't solve the problem I'll try cleaning the throttle body.. if that doesn't work I'll probably replace the coolant temp sensor.

  8. #7
    g60leigh's Avatar
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    also try the N80 purge valve as mine does this when connected, I have disconnected it at the minute and it has stopped.
    I am waiting for a replacement to arrive any day now but has run fine without it for a few weeks

    2001 S3 (AMK)
    AEM WMI Kit, Black Silicone Hoses, Badger5 TIP with Cone Filter, AH Fabrications FMIC, Relentless Manifold Downpipe & Sport Cat, Miltek Cat Back Exhaust, VAG Aero Wipers, Forge FMDV008 Re-Circ, Revo Stage 2 Remap with SPS+ Tweaks, 2.0 TFSI Coil Pack Mod, B&M Short Shift, RNS-D Retrofit, Brembo & B5 2 Piece Rotor Conversion

  9. #8
    Lee Goodall's Avatar
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    Cheers. I'll add it to the list.

  10. #9
    Lee Goodall's Avatar
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    turbo seal is leaking oil but is being upgraded as soon as the running problem is sorted out (boost gauge is reading correct amount of boost too).

    After inspection I have discovered oil leaking around the point where the crankcase breather joins the engine.. previously I have replaced the oil cooler including a new ring seal and replaced the hard rubber breather pipe which I thought had stopped the leak but it appears there is still a problem!!

    Now I'm thinking that this is causing my fuelling problems but I've tried cleaning the entire area and checking to see where the leak is but can't identify the source.. possibly around the base of the oil cooler bracket/engine. Anybody had problems like this before?

    Just want to get on with tuning but this is driving me crazy!!!

  11. #10
    Lee Goodall's Avatar
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    Checked for vac/boost leaks and nothing came to light.

    Cleaned the throttle body, removed the throttle plate too and cleaned the sensor.

    SORTED idles perfectly.. Thanks for to everybody for their input.

 

 

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