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  • Idling problem

    Bit of a strange one here...

    My S50 was generally running fine. About a year ago I started having a really funny idle after full throttle right through the rev range - effectively the idle would rise 1500 - 2500 revs and then back down again, and when trying to drive the car and pressing the throttle there would be a sudden urge forward. Eventually this would clear and the car would be running fine again. I checked the codes and only had injector 4 fault (Which wouldn't ordinarily result in a bad idle!)

    Anyway I put up with it as it was intermittent. After my last run out it's turned out to be a permanent feature from cold start. I took it to my very good ex BMW mechanic and a vanos specialist was also there - both were a bit puzzled. They looked at the codes, pulled the MAF, TPS and Camshaft sensor. They activated the ICV and disabled injectors from diagnostics. Their only conclusion was wiring perhaps.

    Over the years I have done the following:
    • Inspection II
    • Replaced vacuum pipes
    • Cleaned out the ICV
    • Replaced TPS
    • plus many other things I probably can't remember!


    This evening I swapped injector 1 and 4 to see if the fault moved - it didn't. I noticed that injectors 1 and 4 had been marked previously aand swapped. I then looked in the folder and found there was an injector fault on 4 in 2014 and the fault couldn't be diagnosed properly

    Has anyone seen this before? The only 2 things I'm thinking now is either the wiring loom or the DME

    Thoughts welcomed!

    Build thread: https://www.z3mcoupe.com/forum/showthread.php?t=19347

  • #2
    Not sure about the S50 but on other cars idle issues and odd acceleration can be caused by a sticky or failing throttle body.
    ----------------
    David
    1999 M Coupe (S50)
    >>Read my journal here<<
    2005 Smart Roadster-Coupe Brabus
    2022 Range Rover Evoque PHEV

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    • #3
      Oh dear that does sound frustrating, at first glance I can't think of much more than the generic "have you checked for vacuum leaks" and "have you checked earthing points"

      Maybe look up the main earth points and check them for cleanliness and do a wiggle test on the crimp connections/terminals. Maybe you could also check for continiuty and resistance between the ecu multipin connector and each end point.

      Also some sensors tend to work on a 5V reference so if this voltage was low or fluctuating then perhaps that could cause an issue?

      Is it heat related? Wiring and various components can break down with heat...

      Maybe it's the injector loom that needs checking the most carefully?

      Anyway, sorry not much help, but hope you get it sorted!

      Comment


      • #4
        Don't recall ever seeing a bad s50b32 throttle body on the forum, I know that the bar that connects the 3 throttle bodies can bind so may be worth inspecting and oiling all the springs and connections? . I have a used engine loom that is from my 1998 car and is known to be fault free if you want to go down that route.

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        • #5
          Is it with aircon switched on? On my car the throttle definitely feels different with it on as I think it uses the icv to raise revs a bit.

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          • #6
            Might be worth a search on cutters forum as a lot more S50B32 owners on there?

            Comment


            • #7
              I don't think it's the throttle bodies, they seem fine, and I don't think it's vacuum as I replaced them all, but worth another look.

              The ECU is out for testing

              Build thread: https://www.z3mcoupe.com/forum/showthread.php?t=19347

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              • #8
                Any update Martin?

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                • #9
                  Not really. ECU came back clean and tested the injector wiring which seems fine. Need to look intake side I think

                  M2 Competition is providing a useful distraction at the moment!

                  Build thread: https://www.z3mcoupe.com/forum/showthread.php?t=19347

                  Comment


                  • #10
                    Originally posted by mnbrennan View Post
                    M2 Competition is providing a useful distraction at the moment!
                    Hahahaaaaa I was just about to say that I bet you're busy playing with the new toy instead. Looks great mate
                    Not actually in the least bit fat

                    2000 S50 Titanium Silver / Black
                    ACS Suspension, Exhaust & Type III Wheels
                    Simota carbon air intake | Strong Strut Front Brace

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                    • #11
                      Originally posted by mnbrennan View Post
                      Not really. ECU came back clean and tested the injector wiring which seems fine. Need to look intake side I think

                      M2 Competition is providing a useful distraction at the moment!
                      Nice distraction to have , I spoke to a S50 expert and he had a similar issue with a E36 M3 which turned out to be a failed vanos rubber seal he also suggested it may be a bad air leak.

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                      • #12
                        Thanks Dave, some useful pointers. Will be trying to figure this out tomorrow!

                        Build thread: https://www.z3mcoupe.com/forum/showthread.php?t=19347

                        Comment


                        • #13
                          Clutching at straws but maybe you could have the injectors cleaned and flow tested.

                          This isn't actually terribly expensive and usually improves running under light load and or idle, better atomisation and no propensity to stick etc. I did this on a 2001 Maserati 3200 and it did help smooth out the idle and there was good piece of mind.

                          Agree an air leak is more likely though!

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                          • #14
                            I had a very similar problem to what's described , it was a split in the underside of the rubber intake boot in the flexible section , I taped it up with insulation tape first just to make sure that's what it was before ordering a new one .

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                            • #15
                              Feeling like such an idiot. I discounted the Idle Control Valve as it was serviced and working perfectly last year. Took the intake off, had a look at the ICV and it is completely seized up. Raided Stacey's car for hers, fitted it and no more problems.

                              What a numpty

                              Build thread: https://www.z3mcoupe.com/forum/showthread.php?t=19347

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