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M42 rough idle - what am I missing? *Update 3/17 misfire?

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    M42 rough idle - what am I missing? *Update 3/17 misfire?

    Hi.

    Symptoms:


    1. Idle is rough on start-up (excessive vibes, feels like misfire) and lopes like a radical cam V8.

    2. Idle fluctuates between ~750 and 1100 RPM until maybe 15 minutes of run time, at which it still feels a bit rough, but stabilizes.
    3. Fault code 1221
    4. Revs fall a bit too hard after applying clutch. Could use more damped drop off.

    Actions taken / thoughts:

    Air
    1. Vacuum leak
      1. Addressed mess under intake
      2. Checked for leaks with starting fluid
      3. New intake gaskets
    2. ICV
      1. Replaced ICV
      2. Both ICV's pass ohmmeter test
    3. Air filter
      1. Air filter inspected
    4. MAF
      1. Swapped MAF
    Fuel
    1. Injectors
      1. Cleaned injectors
      2. New injector o-rings
      3. Test injector flow?
    2. Fuel filter
      1. Replaced fuel filter
    3. ECU
      1. Replaced Coolant temp sensor
    4. Fuel pump?
      1. Check fuel pressure
    5. O2 sensor?
    Spark
    1. Plugs
      1. Went from Bosch Platinum to OEM NGK
    2. Coils
      1. Swapped Coil packs
    3. Wires
      1. Wires pass ohmmeter test
    Any thoughts?
    sigpic

    #2
    You seem to be on the right track. I would start with swapping the O2 sensor and then move on to fuel pressure.

    How did the old plugs look, was the engine running lean/rich?

    Comment


      #3
      I'll try the O2 sensor.

      Engine is running rich, or at least smells rich. Plugs were not completely fouled, and I saw absolutely no improvement when I installed the new plugs.

      I've googled motronic, but is there a suggested reference? I'm not sure how the O2 sensor would make such a difference at startup.

      I'm going to do a 12V test on the new ICV to address the fluctuation, and I'll check to see if the TPS is stuck in WOT, which I think could explain the richness.
      sigpic

      Comment


        #4
        AFAIK the O2 sensor is not used on startup. But I have heard conflicting remarks. Still, it seems logical that it would be ignored until the CTS says the engine is warm.

        Good thought on the TPS.

        I imagine you have, but did you check the intake boot for cracks/missing plugs (easy to miss with fluid)? As it can cause a stumble at cold idle and be okay once warmed up.

        Have you verified that the TB is adjusted correctly and not sticking?

        Comment


          #5
          when i bought my m42 car it had a loping idle the previous owner replaced everrrything before he did the o2 sensor. upon cold start it really didnt do it but as soon as it warmed up into closed loop it would do it like it was its job. changed the o2 problem fixed idles flawlessly
          e30s r kool

          Comment


            #6
            possibly the m42 hot start problem, there's a thread on m42club.com
            1991 318is ---230K - DD
            1991 318i ---- 308K - retired

            Originally posted by RickSloan
            so if you didnt get it like that did you glue fuzzy oil to the entire thing?

            Comment


              #7
              Originally posted by roguetoaster View Post
              AFAIK the O2 sensor is not used on startup.

              I imagine you have, but did you check the intake boot for cracks/missing plugs (easy to miss with fluid)? As it can cause a stumble at cold idle and be okay once warmed up.

              Have you verified that the TB is adjusted correctly and not sticking?
              I've inspected the intake boot for cracks and missing plugs, but I am not 100% sure it isn't leaking, as I assumed that spraying starter fluid near it would make the engine speed jump. I have a spare that I will try.

              As for the TB adjustment - no, I haven't looked into that - I'll figure out how to do that. I think that's definitely a possible root cause.

              when i bought my m42 car it had a loping idle the previous owner replaced everrrything before he did the o2 sensor. upon cold start it really didnt do it but as soon as it warmed up into closed loop it would do it like it was its job. changed the o2 problem fixed idles flawlessly
              Hmm. That makes sense, but I'm not sure if that would help me since my problem seems to be solved once the temp is at steady state. Still going to try the O2 later this week.

              possibly the m42 hot start problem, there's a thread on m42club.com
              I had tested that before but my situation is interesting. I have no cat (cats?), but I thought that the DME would have a different fueling setup for the euro, non-cat cars, as I think that they can run super lean due to not have to worry about cooking that cat. I may be wrong. I'll try connecting the wire and resetting the DME.

              Thanks for the input, all!
              sigpic

              Comment


                #8
                I think that I can describe this more as a misfire. The lopes quite a bit. Something like "du-du-du..........du-du-du.........du-du-du"

                I swapped in a different TPS and no difference. It may be that they are both bad, but let's assume not for now.

                Swapping the O2 sensor to another used one doesn't help at all either.
                sigpic

                Comment


                  #9
                  did you ever solve this?

                  Comment


                    #10
                    I know this is old but I am very curious if this was ever solved as I am having a similar issue with my M42.

                    Comment


                      #11
                      Originally posted by Bimmerfan84 View Post
                      I know this is old but I am very curious if this was ever solved as I am having a similar issue with my M42.
                      UPDATE: My problem was a new aftermarket crank sensor (Prenco) I installed. Put a BMW one in and it runs perfect.

                      Comment

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