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Thread: Help with diagnosing engine troubles - 1.6 petrol

  1. #1
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    Help with diagnosing engine troubles - 1.6 petrol

    [Solved] Hoping someone can give me some pointers as I'm at a loss with this car after too many hours. Engine is a BGU 1.6. 210,000 km on it. I'm particularly interested if you see a cause that's more likely to cause multiple issues.

    Thanks for reading.

    Problem was caused by a temperature related EGR malfunction. The valve stuck in the open position when hot, but tested normal when cool.

    The main symptom is the engine will sometimes surge at idle (500-1200rpm instead of 700 steady) and become easy to stall. Occurs once up to temperature. This sets off the ASR/Stability lights after 10 min or so. This used to reliably occur 30 min into a drive, due to a leaky PCV hose. Now it's more random. anywhere from 20min-3hrs driving.
    Also:
    Brake boost is randomly gone - Doesn't happen often, the brakes work perfectly again by the next stop.
    Lack of power on acceleration - again fairly rare, no discernible pattern to it. Sometimes even happens on startup.
    VCDS shows different errors by the day. Usually Regulation Deviation in throttle, accel or EGR or Signal Too Low in MAP/IAT sensor.

    My diagnostics of possible causes so far:
    Vacuum leak - no obvious noises of it. Aerosol spray test didn't find anything.
    Intake leak - Intake runner, breather hose and dipstick tube are all new and properly sealed. Secondary air check valve is OK.
    EGR Valve - Checked, has thin buildup of carbon, but valve moves and VCDS adaptation runs fine.
    Ignition - Spark plugs are new, leads are in good condition.

    Untested:
    Variable intake manifold changeover valve - sticking in torque position could cause some issues - read up on this recently, but I'm not sure how to test it.
    Engine-Brake booster vac line - hairline cracks might cause the intermittent loss, but I'm not sure that fits with the other symptoms.
    Wiring harness - no visible damage but I'm not sure how I'd locate problems in it anyway. Ground points look fine on visual check but I haven't removed and reseated any.
    Last edited by ballo; 24-04-2017 at 08:05 PM.

  2. #2
    Super Moderator Lucas_R's Avatar
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    Sounds like you have some potentially dangerous (both to you and other road users/pedestrians) issues. You might be better off taking the car to a VW specialist who can have a good look over everything and run an error code scanner to see where the issue(s) lay.

    I don't think internet diagnosis will work out for you on this occasion.

    Don't take it to VW - waste of time. Find one of the many VW specialist workshops around Melb and take it to them.

    Luckily the 1.6 petrol engine in the Mk5 is a pretty basic setup and relatively easy to work on, so shouldn't take too long for a professional to figure out whats wrong.

  3. #3
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    I was planning on taking it to a tech but with the semi-long weekend I won't be able to til Weds.

    The error codes aren't giving me much help. ABS module gets a DTC code from the engine module, but that's about all that's consistent. IAT and Lambda codes come up sometimes but not consistently, but they could just be symptoms of the engine running poorly from another cause.

    Another forum suggested checking over that booster vac hose but it's a real bugger to get at. Any idea what fastens it to the firewall where it's hidden by the overhang?

    Edit: open sided clips. the first clip engine side faces ↙, the remaining 3 clips face ↓

    Edit 2: No damage, cracks or splits anywhere in the vac line.
    Last edited by ballo; 22-04-2017 at 11:59 AM.

  4. #4
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    New info:
    I checked the measuring blocks while the car was running poorly today. IAT was ranging from 125-132*c.
    The IAT sensor works normally. Reads ambient when cold, warms up to expected temps (sub 80) when running properly.

    Would a stuck open EGR cause high temps at the intake, or am i on the wrong track?

    Solved:
    The EGR is the culprit. Passes adaptation when cool, but once the engine starts acting up it fails.
    I let the engine cool down, ran the EGR valve and then unplugged it once I knew it was in closed position. Car ran perfectly on a long mixed drive.
    Last edited by ballo; 24-04-2017 at 08:01 PM.

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