Announcement

Collapse
No announcement yet.

Infuriating idle issue - ECU fault?

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Infuriating idle issue - ECU fault?

    I'm struggling to diagnose and fix an increasingly frustrating - and expensive - idle issue. So far I've replaced both lamda sensors, and the MAF sensor, as well as cleaning the idle control valve. A diagnostic check has thrown up two fault codes:
    (155) 9B MSS50 Control Unit Fault, fault memory, master
    (156) 9C MSS50 Control unit fault (fault memory, slave).

    It's got my indy stumped, and he spoke with a couple of other specialists who haven't heard of this fault before. Apparently the car is overfuelling, though the obvious symptoms are terrible hunting at idle (all the way up to 2,000rpm, before dropping right down and occassionally stalling).

    Apparently there aren't any air leaks in the system and the cap is in place at the T junction in the airbox.

    Any ideas please? Getting rather desperate (and broke!)

  • #2
    Have you tried the Throttle Position Sensor? It was causing a slight missfire/hesitation on mine between 10-20% throttle. It contains two small wipers which contact with a resistive ring and over time the wipers wear the ring where the throttle is held/used most, i.e. cruising.

    To test it you can just disconnect it for a short time to see if the problem goes away.

    Comment


    • #3
      Originally posted by Brewster View Post
      Have you tried the Throttle Position Sensor? It was causing a slight missfire/hesitation on mine between 10-20% throttle. It contains two small wipers which contact with a resistive ring and over time the wipers wear the ring where the throttle is held/used most, i.e. cruising.

      To test it you can just disconnect it for a short time to see if the problem goes away.

      Thanks Brewster - is there an idiot's guide to where that is located/what it looks like?

      Comment


      • #4
        It's the first sensor you come to when you open the bonnet, on the end of the throttle rail nearest the radiator. It has a small rectangular plug which unclips and pulls off upwards. It's a feed-forward signal for the ECU so running without it won't hurt for a short time. Roughly £60 from a dealer if disconnecting it works.

        Comment


        • #5
          Originally posted by Brewster View Post
          It's the first sensor you come to when you open the bonnet, on the end of the throttle rail nearest the radiator. It has a small rectangular plug which unclips and pulls off upwards. It's a feed-forward signal for the ECU so running without it won't hurt for a short time. Roughly £60 from a dealer if disconnecting it works.
          Not quite idiot enough for me Brewster! But I'll take a look tonight and see if I can work it out from your description. Thank you for responding so promptly.

          If anyone else has any ideas, I'd be really grateful to hear them.

          Comment


          • #6
            Thanks for the tip Brewster - sadly didn't seem to make any difference, but at least I can cross it off the list.

            The adventure continues!

            Comment


            • #7
              These cars!!! have you checked your plugs!!! i know its daft but it sorted mine..as they had not been changed!!! even by bmw!

              Comment


              • #8
                It's on the list to check - but this feels like an air leak issue to me, what with the constant hunting.

                Comment


                • #9
                  Well, it turns out it was an air leak. The cap on the fuel tank vent was missing, and there was also a small crack in the bellows to the plenium chamber (I think that's right?). Anyway, that's fixed the hunting and she now settles as before! Nothing to do with the ECU, thankfully...

                  Comment


                  • #10
                    If its not too much trouble..post some pics of where the leaks were coming from
                    sigpic

                    Comment


                    • #11
                      Originally posted by soma View Post
                      If its not too much trouble..post some pics of where the leaks were coming from
                      I wish I could - but being non-technical, I have no idea!

                      Comment


                      • #12
                        Hey...no worries...glad you got it fixed though
                        sigpic

                        Comment


                        • #13
                          locating these parts

                          Originally posted by W1234 View Post
                          Well, it turns out it was an air leak. The cap on the fuel tank vent was missing, and there was also a small crack in the bellows to the plenium chamber (I think that's right?). Anyway, that's fixed the hunting and she now settles as before! Nothing to do with the ECU, thankfully...

                          Does anyone perhaps know where these parts are in the engine bay?
                          1. cap on the fuel tank vent
                          2. bellows to the plenum chamber

                          I'd be much obliged if someone could point me to the realoem parts...
                          sigpic

                          Comment

                          Working...
                          X