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Lumps and sticky Brakes...

Discussion in 'A3/S3 Forum (8L Chassis)' started by FactionOne, Sep 12, 2004.

  1. FactionOne
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    FactionOne Administrator Staff Member Administrator

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    [Sep 12, 2004]
    Hey folks,

    I'm just wondering if anyone on here could offer me some pointers on a couple of things I'm grappling with at the moment...

    Firstly, I (like many) have been experiencing a bit of a lumpy idle on my A3, I didn't really notice it for a while (it's been off-the-road since I bought it until last week), but I was on the drive fiddling with my audio install, and I had the engine running so as not to drain the battery. Once she'd warmed-up I applied a little right-foot pressure to get th'owd alternator kicking a bit, and when I backed off, I noticed the lumpy idle a little more. The pedal was on the hunt a bit, and at one point quite astonishingly so, when it totally disappeared from beneath my foot (foot was just touching the pedal at idle revs), it returned almost immediately, but carried on its little dance, although not quite as severely. When this most noted 'choppiness at idle' happened, the revs were jumping between anything from 700 up to maybe 1200.

    Anyway, I decided I'd give the MAF a clean (although she's only just done 35,800 miles) - I did this (using electrical contact cleaner and only the pressure of the spray to loosen any deposits), and after foolish3uk advised that a "basic setting" is recommended after a flat battery (which has happened - new stereos are a b***h! /ubbthreads/images/graemlins/wink.gif), I did some more reading and figured this to be mainly aimed in such a case at re-alignment of the throttle valve control unit. I found out this could be done with VAG-COM and did that after the MAF clean.

    After those two measures, things seemed to be about 99% improved, and when I finally got her taxed and insured, I went out for a bit of a test run with my old man, with me in the passenger seat at the helm of a laptop.
    It looked like the MAF was reading plenty of air, and all the figures looked pretty tidy. All in all, she was running pretty well (bar the driver's corner brake - more on that in a minute /ubbthreads/images/graemlins/wink.gif).

    The remainder of the lumpy idle thing is really starting to annoy me now, in that I'm at a loss for ideas. It's almost as if there's a slight mis-fire happening, well, so my ears are trying to convince me anyway. There's a definate uncertainty audible from the engine, and the same when you're round the back listening to the exhaust (although I must admit, it's almost nice from that end! /ubbthreads/images/graemlins/lol.gif).

    I thought I'd take some data today, and post it up here in case someone could suggest things I should perhaps be testing. I've attached an excel file of some data I collected in an idle period this afternoon - starting momentarily after the engine settled off 'choking' until a little while after the laptop reported approx. 90 degrees (which was a good few minutes after the temperature gauge on the dash btw).
    I've done some sketchy plots of the data recorded, to maybe give a better illustration of what's happening.

    Sheet 2 shows approximately 4 minutes worth of data (if my maths isn't failing me!) - while the temperature was passing around the 80C mark. This gives a reasonable representation of what's going on, with peak at 836RPM and minumum at 736RPM (approx.)

    Sheet 3 shows the last minute before I turned the enine off, the peaks in this plot are a little lower, but the drops are to similar levels. Engine feedback (both audible and vibration felt through the wheel) was the same.

    Sheet 4 shows all the data captured, for an 'at-a-glance' view of everyhing, including the highest peaks, lowest drops, and the frequency of fluctuations.

    --

    The second question I have is perhaps simpler in mechanical terms - A short while ago I noticed that the brake in the driver's corner was a little reluctant in letting go when I put her to bed in the garage after work - presumably because of a prolonged period of sitting in the garage doing nothing. It wasn't by any means a tight grip, however the piston was far out enough for the pads to rub the disc.

    When we went out for a run checking the MAF, and the general behaviour of everyhing, there was a bit of noise coming from it, but after a while this seemed to ease-off, and with a bit of dabbing the brakes, the piston seemed to be returning further. The car was quite able to maintain a roll along flat, or even slightly inclined road with the clutch in.

    However... the problem is still there to an extent, as there's a slight rubbing noise as the car rolls to a stop, the wheel in that corner was warmer than its opposite, and when I removed the wheel today to have a look, I found pads rubbing the disc slightly.
    I was going to remove the pads etc. to get a better look, and perhaps a decent opportunity of lubricating the piston, but the hex-key bolts on the caliper soon put a stop to that (they're pretty determined to stay in-situe, and it started p*****g down just as I was starting to get really fed up with them).

    So my question is this - does anyone know of any sneaky tricks I could try to alleviate the problem and help the piston return all the way? Or even how I have a decent chance of loosening the hex-bolts ot get the caliper off if that's the only route I have (without windy-tools, a gas-axe, or a pentogram and black candles!).

    As always any help you guys can offer would be gratefully received, and again as always, I'm sorry for waffling-on so much!

    Thanks and regards,

    Rob.
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