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Poor Running, Worse Cold - Never 100%

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  • #16
    Check the intake air temp sensor in the afm.

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    • #17
      OK... I went out right before a killer Maui sunset while I still had light, pulled the cover and fired up the car.

      Flexing the short, before it disappears, harness did not make any visible/audible/smoothness difference in the idle. I pulled the plug from the sensor and again, no difference.

      I am not sure if this indicates much... thoughts?
      "The earth provides enough for everyone's need. Not everyone's greed." Gandhi

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      • #18
        Originally posted by indie_wannabe View Post
        Check the intake air temp sensor in the afm.
        I'm thinking that my bud did check the resistance on that sensor.. I need to look back.

        Do you recall the desired resistance range?
        "The earth provides enough for everyone's need. Not everyone's greed." Gandhi

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        • #19
          Originally posted by MauiM3Mania View Post
          I pulled the plug from the sensor and again, no difference.

          I am not sure if this indicates much... thoughts?
          It has been a few years since I had to mess with my Coolant Temp Sensor, but if my memory is correct I believe that the idle would rise significantly (very noticeable) if it was unplugged (it was seen as a very high (= cold) resistance).

          If you experience no difference when unplugging the sensor while running I would suspect that you have an open in the cable. If you have a multimeter with fairly long leads you should be able to measure continuity from from the plug end in the engine compartment to the DME (engine computer) end under the dash.

          Good luck!
          Dominic

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          • #20
            Originally posted by MauiM3Mania View Post
            I'm thinking that my bud did check the resistance on that sensor.. I need to look back.

            Do you recall the desired resistance range?
            I'm sorry but I don't think I can be much help here. I suggested you check the temp sensor in the AFM because the BMW mechanic told me mine was bad when my car was acting similarly to yours. I think they told me I needed to get a new AFM to fix the problem. Honestly I didn't pay a lot of attention or look into it much myself since I was getting ready to switch to Alpha-N at the time. I wasn't going to spend money on a new AFM when I was going to be removing it from the car soon anyway.

            As I remember, he told me that the bad intake temp sensor was off more when the car was cold and made the car run even worse at start up. After the sensor was heat soaked and warmed up, it was still giving inaccurate readings but not as badly as when it was cold. I'm not sure the mechanic's explanation was spot on, since I didn't verify it myself.

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            • #21
              Originally posted by indie_wannabe View Post
              I'm sorry but I don't think I can be much help here. I suggested you check the temp sensor in the AFM because the BMW mechanic told me mine was bad when my car was acting similarly to yours. I think they told me I needed to get a new AFM to fix the problem. Honestly I didn't pay a lot of attention or look into it much myself since I was getting ready to switch to Alpha-N at the time. I wasn't going to spend money on a new AFM when I was going to be removing it from the car soon anyway.

              As I remember, he told me that the bad intake temp sensor was off more when the car was cold and made the car run even worse at start up. After the sensor was heat soaked and warmed up, it was still giving inaccurate readings but not as badly as when it was cold. I'm not sure the mechanic's explanation was spot on, since I didn't verify it myself.
              I have a similar problem with my car, where it stutters badly for about 60-90 seconds after cold start up when I try to drive it. I was told by my mechanic also that it was most probably the AFM for the same reasons given above. Have not gotten around to fixing it, as I just let the car warm up and everything is fine.

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              • #22
                Subscribing....

                I have some of these same symptoms. I'm pretty sure my air temperature sensor is bad, as I described in http://www.s14.net/forums/showthread.php?t=50336

                I would fix the IAT but it seems like I should consider options like alpha-N or MAF, so that's what I'm doing.
                1987 Euro M3, Jet Black
                "BMW M cars: technically advanced, beautifully engineered, and the choice for total gits" -- Top Gear, Summer 2008

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                • #23
                  Further update:

                  On a hunch, I pulled the DME to discover a rat had pee'd on the thing. :rains:

                  I pulled the DME from the parts car and installed it in the driver.

                  Cold starts are 100% better, still has a minor hickup here and there, but is night and day. Once at operating temp, the car runs smoother as well, has lost the surging and definetly more power. I even feel a kick in power around 4K at WOT. :woohoo:

                  I'm thrilled. I feel that this is pretty darn close to correct... 95% if not 100%. This is good as a Miller Performance MAF conversion is going in soon. Hopefully, this may address any present or potential issues caused by the AFM and the IAT sensor.
                  "The earth provides enough for everyone's need. Not everyone's greed." Gandhi

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                  • #24
                    What's a DME?
                    There'll be Spandex jackets one for everyone ...

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                    • #25
                      Basically, it is the computer that runs the car. Some refer to it as the ECU. Some as the brain. Some call it the magic box. Some people call it the main behind the curtain.

                      I just call it the aluminum cased box of electronics with rat pee on the outside top.
                      "The earth provides enough for everyone's need. Not everyone's greed." Gandhi

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                      • #26
                        Thanks. I wanted to verify because the same thing happened to me except it was mice not rats.
                        There'll be Spandex jackets one for everyone ...

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                        • #27
                          Originally posted by indie_wannabe View Post
                          After the sensor was heat soaked and warmed up, it was still giving inaccurate readings but not as badly as when it was cold. I'm not sure the mechanic's explanation was spot on, since I didn't verify it myself.
                          There wont be any heat soak in that sensor as it would make that a crap sensor. So by design they will make sure that whatever the surround temperature of the material the sensor is mounted in, it will still measure the temp of the air it sits in (more or less) precisely. In other words, as soon as air with a different temperature starts moving past the sensor it will register that.

                          repairing a temp sensor in the AFM might not be easily possible but I would try to rig in an external one as used on the aN-setup and wire that to the appropriate terminals of the AFM (1 and 4). I reckon it will have the same resistance/temp-curve as the sensor inside the AFM.

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                          • #28
                            Originally posted by hardtailer View Post
                            There wont be any heat soak in that sensor as it would make that a crap sensor. So by design they will make sure that whatever the surround temperature of the material the sensor is mounted in, it will still measure the temp of the air it sits in (more or less) precisely. In other words, as soon as air with a different temperature starts moving past the sensor it will register that.

                            repairing a temp sensor in the AFM might not be easily possible but I would try to rig in an external one as used on the aN-setup and wire that to the appropriate terminals of the AFM (1 and 4). I reckon it will have the same resistance/temp-curve as the sensor inside the AFM.
                            Hardtailer...Clean your pm space...
                            I've sent you an email from a non hotmail account.
                            power is nothing without drift

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                            • #29
                              Originally posted by france320isco View Post
                              Hardtailer...Clean your pm space...
                              I've sent you an email from a non hotmail account.
                              Thanks for letting me know. I cleaned it out and replied to your mail.

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                              • #30
                                Strangely, the cold running issue has gradually returned. When at operating temp, it still runs much better than before the DME swap. But for the first 90 or so seconds, it idles terribly and surges under load.

                                I don't get it! And no, the rat did not return.
                                "The earth provides enough for everyone's need. Not everyone's greed." Gandhi

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