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  • Boost/Idle issue

    Hi all, new to the UrS club. I picked up a running 95 emerald green avant with 172k for $1500 and I am trying to figure out an odd boost issue. When driving the car, it revs to about 4000rpm in 1st and feels like its hitting a brick wall, starts stumbling and almost stalling. The engine also surges at idle when warm and smoke comes from the exhaust (as if running rich). I hooked up a boost gauge, tapping into the Motronic feed. At idle and coasting, I still get 10-20" Hg vacuum but pinned on 0 psi boost when accelerating and barely 1-2 psi in 2nd gear before hesitating and cutting out at around 2500rpm. There are no codes shown on VCDS except for the Lambda (00537 - Control Limit not reached). Ive searched around the engine bay and I cant spot any obvious boost leaks; there was an FMIC installed and the hoses seem to be secured well. I also upgraded the stock POS' to LS coils and a DIY wire harness with no changes to my issue.

    The state of the car when purchased:
    - the wastegate was removed and the ports were blocked off
    - I removed the plates, cleaned checked the diaphragm and reinstalled the wastegate.
    - FMIC was installed
    - secondary air system was deleted and the hose on the turbo inlet pipe was blocked off
    - K&N cold air intake filter was installed
    - stock POS' were replaced with other stock ones
    - I replaced them with LS coils and wires
    - cat delete and full 3' exhaust from the downpipe with a Vibrant muffler
    - (apparently) a stage 2 chip on the ecu for 350 hp
    - lowered on H&R lowering springs

    I was thinking the MAF could be the issue but not entirely sure, any and all suggestions welcome.

  • #2
    Boost leaks can be a nightmare to find, keep looking you will find some the symptoms sound like a boost leak

    Comment


    • #3
      You really need to do a proper leak test by pressurizing the inlet tract with compressed air and spraying soapy water on all the boost hoses etc
      Search the forum,there is a how to thread somewhere
      Also nice going getting a running urs for $1500!!
      It's a love/hate relationship with the S2,i love it,it hates me

      Comment


      • #4
        Certainly sounds like the classic symptoms of a boost leak.
        91 Modded 3B
        14 A6 Avant Black Edition

        Comment


        • #5
          If the car had been run without a wastegate I’d be looking to see if the turbo is still functioning!

          S2 Coupe 3B Project


          Ur quattro restoration

          S2 Avant

          Boost is the new rock and roll!
          sigpic

          Comment


          • #6
            Unless a different turbo with a built in WG like a K04 has been fitted?

            S2 Coupe 3B Project


            Ur quattro restoration

            S2 Avant

            Boost is the new rock and roll!
            sigpic

            Comment


            • #7
              Thanks for the responses everyone, I did indeed find quite a large boost leak coming from a couple of tears in the crossover pipe. One was only visible from under the car and the other under a clamp. Grabbing one from a junkyard tomorrow, wish me luck!
              IMG_5684.jpg
              IMG_5685.jpg

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              • #8
                Originally posted by newsh View Post
                Unless a different turbo with a built in WG like a K04 has been fitted?
                No its got the stock K24, po took off WG thinking it was stuck open. And i sure hope its still good, guess we'll find out once the crossover pipe gets replaced

                Comment


                • #9
                  That's certainly going to cause a massive boost leak!
                  91 Modded 3B
                  14 A6 Avant Black Edition

                  Comment


                  • #10
                    I'm surprised the smoke test and pressure test did not point you to this although happy you have got to the bottom off the problem with the car. Now its out for a . Best wishes Lynn

                    Comment


                    • #11
                      If there are no leaks the inlet tract will hold 1Bar for 30 seconds or so, maybe more.
                      There will be a little air getting past valves and piston rings obviously so it won’t hold indefinitely.
                      With a big leak like that you will get no pressure at all.
                      It’s worth disconnecting the breather system from the MAF hose when you do the test to rule out problems with the one way valve under the IM.

                      S2 Coupe 3B Project


                      Ur quattro restoration

                      S2 Avant

                      Boost is the new rock and roll!
                      sigpic

                      Comment


                      • #12
                        Good news, the new hose fixed the revving issue and the idle surging, bad news I now get no more than 5 lbs of boost on full tilt. Ive pretty much ruled out any possible other boost leaks so maybe a bad N75?

                        Comment


                        • #13
                          Disconnect the N75 and run the car to see if it makes any difference.

                          With engine idling. Put your hand on the N75 (if you can reach it) and blip the throttle, can you feel it vibrating?

                          Make sure the vac line is connected to the ECU and there are no leaks in it. Best to test with a mightyvac from the engine bay.

                          Disconnect the MFTS and see if you get your boost back, URS doesn’t normally restrict boost when this sensor goes wrong but who knows..

                          S2 Coupe 3B Project


                          Ur quattro restoration

                          S2 Avant

                          Boost is the new rock and roll!
                          sigpic

                          Comment


                          • #14
                            Maybe your wastegate as to much shaft play and doesn´t seal and doesn´t hold boost! Maybe that is why it was removed!

                            Had that problem!

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                            • #15
                              Soo update time. Ive been doing a large number of things to the car including a new timing belt kit and billet cog and more boost leak testing. Ive found no more obvious leaks and for the first few minutes of driving i get up to 16-17psi but once the car warms up and i come to a stop and go again, back to only 5psi. I suspected an issue with my tps since my idle was funky and sure enough there is no continuity between pins 4 & 6 and no audible clicking when opening the throttle slightly. Could my boost issue possibly be related to a bad tps, or will that only address my idle problem?
                              Also i spoke briefly with Marc @EFI and showed him the codes I got and he claims a vacuum leak could most likely be the culprit of my boost issue since i have both the lambda control limit not reached and maf codes, causing the ecu to go into limp mode when dealing with boost. Might just take it to him to have him do a smoke test
                              codes.PNG

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