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Recent S50 swap - intermittent idle issue

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    Recent S50 swap - intermittent idle issue

    So I've had my S50 swap running now for about 6 weeks, and in the last week or so I have developed an odd idle issue that pops up intermittently.

    The first 3 weeks or so my VSS signal was not getting to the ECU and the idle issue was not present. Now the car will once or twice a day decide that it doesnt want to idle properly.

    It will only do it when you clutch in and the car is moving - revs will go from about 400-900 constantly until you come to a stop and it settles down to a normal idle. On one occasion it didnt catch the drop and the car stalled. Ive checked for vac leaks and cant find any - most vac hoses were replaced when the engine was put in, ICV cleaned, PCV connector and O-ring is new.

    Problem is that I cant get it to start doing it on demand, so it makes it hard to test. Car isnt throwing any codes apart from tank venting system (its not plugged in and canister vents to atmosphere and bottom of TB is plugged)

    Anybody seen issues like this that are intermittent?
    90 318i M62B44 OBD1
    02 530i Touring (Airlift 3P)

    #2
    yes, quite a few people have had this happen actually. Mine has done it twice. Both times it happened in my neighborhood, coming to a downhill stop sign and pressing the clutch around 30mph.

    just for reference, I have a chipped red 413 dme
    '87 325ic, powered by S50.

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      #3
      Im running a chipped silver 413 with TRM tune for 24lb injectors and euro HFM.

      It did it today in traffic, got so bad it stalled once and then when i started it back up it felt like i was missing 95% of my usual torque below 2000rpm (didnt matter how much throttle i used it was slow as hell). Above 2000rpm it took off as though a switch was flicked....

      Going to try another TPS and I have a new O2 sensor to put in on the weekend.
      90 318i M62B44 OBD1
      02 530i Touring (Airlift 3P)

      Comment


        #4
        Originally posted by wakdog View Post
        Im running a chipped silver 413 with TRM tune for 24lb injectors and euro HFM.

        It did it today in traffic, got so bad it stalled once and then when i started it back up it felt like i was missing 95% of my usual torque below 2000rpm (didnt matter how much throttle i used it was slow as hell). Above 2000rpm it took off as though a switch was flicked....

        Going to try another TPS and I have a new O2 sensor to put in on the weekend.
        Any update on this?

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          #5
          Mine does it with a/c load mostly but other times it did it as well. After sometime it goes away completely and the only time it comes back is when i take my hfm or air filter off. No vac leaks either. The hfm is extremely sensitive from what i can tell. If you hit it with your hand during running it can surge same way. Also besian says on their site that irratic idle can be caused by bad vanos seals. I just replaced mine and on first few drives it still did it although very very slight.

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