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suggestions for best diagnostics for 99 mcoupe midlands

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  • suggestions for best diagnostics for 99 mcoupe midlands

    Hi all, I have a s50 M coupe, I have an intermittent idle issue once warm, from cold start its idle is pretty steady around 650, however from a restart the idle can sometimes die, but before it does it might bounce up and down a bit, but again this is intermittent.

    The car is running better and better the more I use it and have run injector cleaner through which helped, goes really well and doesnt seem to struggle with low down torque.

    I havnt looked at idle control valve or breather hoses yet, but thought before I do what sort of information can be gained from a full diagnostic scan? Would it tell me if an o2 sensor or something else along those lines is faulty. I have had it scanned but looking at the paper work it was a quick scan and showed no faults other than a few relating to perhaps having a flat battery.

    If it was an air leak I would have thought it would be a constant idle issue, but as its from a restart and hence at this point using the onboard sensors to inform the ecu whats going on, it could well be a sensor, and hence a full scan could show this up.

    Would the idle control valve lead to a fluctuating idle from cold?

    If anyone could recommend someone who could carry out a full scan somewhere close to Nottingham would be appreciated. Thanks guys, Dave

  • #2
    You are probably aware, but if you buy a 16 pin to 20 pin adapter you can attach it to the round diagnostic port in the engine bay, and then connect a generic OBD code reader to read codes.

    Whilst not as full as a BMW factory system this should give you most codes.

    You can get this setup very cheaply, or for mid price I like the Autel Code reader I have, it even lists the M Coupe and S50 coupe in it's menu.

    Otherwise I'm sure someone can check it out for you, but not familiar with the Notts area.

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    • #3
      I had a minor idle issue that was solved by a 75p rubber cap, it’s a tiny cap on the right side of the engine bay as you look at it. Here is a thread link below:

      https://www.z3mcoupe.com/forum/showthread.php?t=9557


      I’m sure at one stage this was a well known problem. I’m not saying it will solve your fault, but it’s worth checking as I had an uneven idle that disappeared after fitting this rubber cap, they disintegrate over time.

      Link to part number:


      https://www.realoem.com/bmw/enUS/sho...diagId=13_0442

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      • #4
        Thanks guys

        As the idle problem could be many things I spoke to Rob at Autobahn, on the recommended mechanic section on the forum, who also has his own coupe. He seems like a nice chap and knows his stuff. He explained it could be a few things and has the diagnostics to check out the car.

        So I'm booked in :) I would sooner find what it is than try lots of different stuff and maybe find the solution after changing parts that are good.

        Thanks for advise and links guys, enjoy the sunny weather :)

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        • #5
          let us know how you get on

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