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  • Revs Dropping When Slowing Down

    I've broken it already!

    ​When coming to a stop the revs dip to around 500rpm, jump just past 1000rpm and then settle where they should. Doesn't do it when revving at idle, but it does feel like it has an every so slight hesitant idle.

    Is it possibly related to the bomb or a vac leak?

    Just wondering best places to start looking.




  • #2
    Broken what?

    Comment


    • #3
      Do a search on ISV idle stabilisation valve loads of info on here with same symptoms. I’d clean it first before condemning

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      • #4
        Originally posted by andyg plym View Post
        Do a search on ISV idle stabilisation valve loads of info on here with same symptoms. I’d clean it first before condemning
        Cheers, a few others have said that and it seems easy enough so i will give it a go this week.

        Comment


        • #5
          I have a known good ISV if needed. Vac leaks can also cause this so check so for persisted lines

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          • #6
            Sounds lie the ISV, use brake parts cleaner to give it a good clean, then finally once all that's evaporated give a it couple of squirts of WD-40 so it's got some lubrication, I find them more reliable if you do that as opposed to if you put them back on totally dry.

            As mentioned could also a vacuum leak but I'd clean the ISV first.
            1989 B3 2.0 3A 80 quattro. Long term project.
            1992 C4 100 2.8 Avant quattro, daily driver.
            1995 RS2, MTM K26/7, 380 BHP conversion.
            1997 C4 2.8 30V quattro, currently breaking for spares.
            1991 MK2 Golf G60. For sale.
            1990 Corrado G60. Looking sad.

            Comment


            • #7
              Cheers all, I'll go ahead and give the ISV a clean and see how it goes.

              Other than that still loving the car, drives so well for an old thing!

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              • #8
                The bottom clip on the ISV is tricky! Gonna get it off and replace it with a jubilee clip.

                Any tips for the bottom hose or is it just a bit fiddly in the small space?

                Comment


                • #9
                  So cleaned the ISV out and replaced some hose clamps that were missing, it seems a little better but still not 100%.

                  With the ISV unplugged the issue seems none existent, so am i right in thinking I need a new ISV?

                  Comment


                  • #10
                    The ISV's are normally very reliable and respond well to cleaning, though like anything mechanical they can eventually fail, I'd try cleaning it again once more to be 100% before picking up a second hand replacement.

                    Nice thing is they're not too hard to find as Audi used that ISV on a lot of other engines, the one on my old B3 K-Jet 2.0 quattro saloon is the same for instance and it looks like Monkey has one to hand.
                    1989 B3 2.0 3A 80 quattro. Long term project.
                    1992 C4 100 2.8 Avant quattro, daily driver.
                    1995 RS2, MTM K26/7, 380 BHP conversion.
                    1997 C4 2.8 30V quattro, currently breaking for spares.
                    1991 MK2 Golf G60. For sale.
                    1990 Corrado G60. Looking sad.

                    Comment


                    • #11
                      Originally posted by K Simmonds View Post
                      The ISV's are normally very reliable and respond well to cleaning, though like anything mechanical they can eventually fail, I'd try cleaning it again once more to be 100% before picking up a second hand replacement.

                      Nice thing is they're not too hard to find as Audi used that ISV on a lot of other engines, the one on my old B3 K-Jet 2.0 quattro saloon is the same for instance and it looks like Monkey has one to hand.
                      Already done it twice, first time used brake cleaner and lubricated with GT85.

                      Second time almost a full can of WD40 through, also blocked off the inlet and filled it to the brim with WD40 and left it 30 mins, then some GT85 to keep it lubed and atill seems the same.

                      It has definitely got better, but it isn't 100%.

                      With the ISV unplugged the idle issue doesn't happen, but it does become jerky to drive so its lead to me believe it is faulty.

                      I would like a new unit but only onws are new ebay specials, but it seems these have been working for people? Suppose its worth a go, buyer protection is good and one high rated seller offers 5 years warranty on a £32 ISV!


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                      • #12
                        Yep, sounds like you've well and truly tried cleaning it and if it kinda behaves itself unplugged then replacement one it is.

                        £32 sounds like a bargain, I did say it's pretty generic part used on many models, is that for a Bosch unit or another make?
                        1989 B3 2.0 3A 80 quattro. Long term project.
                        1992 C4 100 2.8 Avant quattro, daily driver.
                        1995 RS2, MTM K26/7, 380 BHP conversion.
                        1997 C4 2.8 30V quattro, currently breaking for spares.
                        1991 MK2 Golf G60. For sale.
                        1990 Corrado G60. Looking sad.

                        Comment


                        • #13
                          Originally posted by K Simmonds View Post
                          Yep, sounds like you've well and truly tried cleaning it and if it kinda behaves itself unplugged then replacement one it is.

                          £32 sounds like a bargain, I did say it's pretty generic part used on many models, is that for a Bosch unit or another make?
                          Sadly just an unbranded unit, it seems the Bosch ones are NLA.

                          Comment


                          • #14
                            So, keeping an eye boost today and I'm not getting more than PSI 
                            ​​​​​​​Would a boost leak cause a hesitant idle? It just seemed strange that the ISV being unplugged sorted the dropping revs issue.

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