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ISV Clean Due to Erratic Idle

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  • ISV Clean Due to Erratic Idle

    Just thought i would let you know that i had a very erratic idle on my RS2 over the last 3 or 4 weeks, it used to happen before the engine had got up to full engine running temperature, so though i would take it off to have a look at it and found it was sooted up inside, no carbon/oil build up, just the soot. Had a look around on Google and found a few articles on cleaning also looked at new ones, OEM/Bosch ISV`s are shown at around £185, a none OEM is available on ebay at around £30. Anyway thought i would give it a clean first to see what the results were, so took it off of the car which took all of about three minutes a few sprays with carb cleaner and some shaking up with the cleaner inside and much black liquid coming out, I ran the cleaner though the ISV until it appeared to be clean and refitted it. Took it out and now drives once more as it should.

    When the engine was warming up and i used to come to a junction and to idle, the revs would drop very low or the engine would cut out all together, now when coming to a stop it drops to 850rpm and holds, Im really pleased its such and easy and cheap fix.

    You will see in the first picture that it doesnt take a lot to slow the ISV down, the rotary valve is only just covered in soot but you can see "contact" scraping marks on the valve, whereas on the second picture its totally clean.

  • #2
    Yup, this is one of those easy solutions to a common problem. Glad it worked well for you.
    Find me on Instagram @pry4sno
    2010 Golf Sportwagen TDI /// #farmenwagen
    2002 Dodge Ram 2500 24v Cummins 4x4
    1992 80q 20v /// Eventual AAN'd Winter Sled
    1990 Cq /// Project: Because Racecar

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    • #3
      Yes the hardest part of the whole job was getting to the jubilee clip on the bottom hose connection, which probably took about 90 seconds to do. Well pleased with the results.

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      • #4
        Good result
        You should lubricate it with some ACF50 / GT85 or similar - powerful solvent like carb cleaner is great to revive them but they wear quickly and start sticking if you don’t lubricants them
        Panthero Coupé quattro 20vt
        Indigo ABY coupé
        Imola B6 S4 Avant

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        • #5
          Originally posted by Error404 View Post
          Good result
          You should lubricate it with some ACF50 / GT85 or similar - powerful solvent like carb cleaner is great to revive them but they wear quickly and start sticking if you don’t lubricants them
          I've been advised to avoid a silicone-based lubricant, is that accurate?
          Find me on Instagram @pry4sno
          2010 Golf Sportwagen TDI /// #farmenwagen
          2002 Dodge Ram 2500 24v Cummins 4x4
          1992 80q 20v /// Eventual AAN'd Winter Sled
          1990 Cq /// Project: Because Racecar

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          • #6
            Mine has managed 116k miles since its first clean yesterday so i will wait for it to happen again then look into lubing it, if it needs it.

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            • #7
              I cleaned the working parts on mine by dangling it in an ultrasonic cleaner. Couldn't be any cleaner and it worked perfectly... Until it had stood for a while. The behaviour could best be described like a bouncing misfire. Revs go up splutter splutter, revs droop and repeat.

              Cleaned it again and added some lube and all is good. If you think about how little carbon it took to slow down the sliding valve, you can see that it won't take too much friction on the dry or potentially oxidising Bush to also slow it down again...

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              • #8
                Ive had to do this, I cleaned it with carb cleaner and cycled 12v from a motorbike battery to it while spraying cleaner. Did the job for a while but occasionally its started to stall again. Electronic throttle is the way forward so that I can ditch the old components once and for all. Less clutter in the bay

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                • #9
                  Use VagCom test and spray with carb cleaner
                  photobucket SUCKS
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                  • #10
                    PRY4SNO,

                    Yes sir, similar to the need to ensure only O2 "sensor-safe" silicone sealants are used upstream.

                    https://www.sae.org/publications/tec...ontent/860478/

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                    • #11
                      I need to do mine again on the Avant, I usually wash out with WD40 or similar.
                      might try brake cleaner and then lube with ACF50 this time.

                      S2 Coupe 3B Project


                      Ur quattro restoration

                      S2 Avant

                      Boost is the new rock and roll!
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                      • #12
                        OK an update on this issue, after about a week of running ok the problem returned, so cleaning the ISV had kind of sorted the issue but it hadnt erradicated it totally, I lived with an erratic idle for the last few weeks then it started to get worse. The car was idling all over the place, up to 1,500rpm, 400rpm and also stalling at junctions or whenever i came to a stop, so decided that maybe the ISV was 25 years old and a new one was required, i bought a new one, fitted it and all the problems were still there. So this morning i decided to attack all the hoses and see if any were split or holed, i also had some Carb cleaner to check for holes as this would have indicated a leak if the engine revs increased significantly, I squirted all around the hoses and found nothing, other than not finding any leaks it certainly cleans the parts pretty well. After not finding much i then decided to take off the major air pipes and check around where the jubillees fit to see if i could see any cuts/holes (that sometimes appear from tightening a jubilee too tight) in the rubber pipes, i found nothing.

                        However when i took of the inlet pipe to the throttle body, i could see there was a small build up of black matter on the face of the thottle plate and this was slighlty holding the throttle plate open and not allowing it to close fully, i gave it a clean with carb cleaner and got all the sticky gunk off and started to put all the hoses back on, plus the old ISV. Restarted to engine and now works perfect, idles correctly and no increased revs or stalling. I wish every fix was as easy as that.

                        Thinking about it the trottle body sensor was possible not seeing fully closed everytime due to the build up, therefore the ISV was not getting a signal from the ECU to open and allow a good idle speed. Might be something else but thats just my thoughts on it.
                        Last edited by rustybullethole; 28th July 2020, 14:14.

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                        • #13
                          That all sounds very plausible, good find, and cheap once you found the real issue!

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                          • #14
                            Yes I`m pleased i found that, ive been out again in the car and starting from cold this time, all is good. I just have brand new spare ISV now, which i will hang on to just in case, it wasnt too expensive.

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                            • #15
                              Thanks for the update...
                              The Perfectionist
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                              Audi Class Concours winner Stoner Park 2014, ADI Concours D'Elegance Class Winner 2008, Runner up 2014. Winner, S2Forum Show'n'Shine Billing 2006 & 2008.

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