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    Very rich/rough idle

    My car has had a rough idle for a while. I know it had vacuum leaks at the seals on the crank case vent tube. Recently replaced the head with a rebuilt head and replaced all seals, etc. that came with the kit. At the same time, replaced the c191 connector with a weather pack connector.

    The idle is now worse than before and there is a slight miss at low RPM's (1000 to 1800). Runs great at WOT. Sometimes hard starts cold or hot. Very rich at idle, could be due to missfire or bad fuel management, not sure which.

    I'm looking for ideas for things I might be forgetting about or something I may have missed in my trouble shooting process. See below for details.

    Setup
    M20B25 - stock short block
    Rebuilt Head with Schrick 272 cam
    Headers
    17# injectors
    Mark D chip

    Steps Taken so far
    Smoke tested - no leaks
    Swapped AFM - no change
    Swapped ICV - no change
    Checked all harnes/sensor connectors - clean and connected tight

    Next steps
    Swap ECU to a stock spare, maybe even swap chip to other ECU
    Test or replace Temp sensor
    Test TPS - still clicks, but I haven't tested resistance yet
    Compression test
    ???
    90 325i DD/Track
    03 Durango 5.9


    Originally posted by e30mpg
    It is recommended to get new gasket but this is R3v and we just copper spray that shit......slap biotch on and tighten to tq.

    #2
    I'm running pretty much the same setup you are except with a ported 731 head with a 272, and been having the same issues you are. We tested my fuel pressure and i am running at nearly 90psi. Dropped to about 46psi when we ran a hose from the regulator into a gas can. We found that my return line running inside the gas tank is clogged. I have an 89is with the 63 liter tank that the return line enters the tank behind the filter, not on top by the pump. Feels like the clog is about 10 inches in.
    sigpic

    Comment


      #3
      Thanks, it had slipped my mind that too much pressure can cause rough/rich idle. So easy I forget my past days of carburated motors. I will definitely check fuel pressure.
      90 325i DD/Track
      03 Durango 5.9


      Originally posted by e30mpg
      It is recommended to get new gasket but this is R3v and we just copper spray that shit......slap biotch on and tighten to tq.

      Comment


        #4
        Update:

        Tested fuel pressure, steady at about 36 to 37 psi. Drops about 4 psi when revving in neutral.

        I will swap to a completely stock ECU later today to see if that helps. Still need to test TPS, temp sensor, and CPS for ohms.
        90 325i DD/Track
        03 Durango 5.9


        Originally posted by e30mpg
        It is recommended to get new gasket but this is R3v and we just copper spray that shit......slap biotch on and tighten to tq.

        Comment


          #5
          Another Update:

          Swapped ECU's, no improvement in idle.
          90 325i DD/Track
          03 Durango 5.9


          Originally posted by e30mpg
          It is recommended to get new gasket but this is R3v and we just copper spray that shit......slap biotch on and tighten to tq.

          Comment


            #6
            m20 idle

            It's that volvo lip and black grill causing the Idle issue.

            Comment


              #7
              Originally posted by brickwhite View Post
              It's that volvo lip and black grill causing the Idle issue.
              Hey! you leave that sweet azz setup alone it makes me jelly cause my car is a beater right now lmbo.
              sigpic87 325E The Honey Badger

              Comment


                #8
                O2 sensor bad? TPS adjusted wrong/bad?

                Comment


                  #9
                  If it's running fine at WOT, then there is something wrong with your closed loop operation.
                  WOT is ran on open loop and ignores the values it receives from the o2 and coolant temp sensor. Open loop is ran off of set values stored on the ecu, you can force open loop by running your motor with the o2 disconnected. In the case of motronic, the coolan temp sensor actually gives more useful information to the ecu than the o2 sensor.
                  Does the rough idle disregard whether the motor is dead cold or hot?

                  Comment


                    #10
                    I'm following this thread because I'm in the exact same boat, just haven't swapped as many parts out yet and I do still have a TINY vacuum leak at the crankcase vent. Rough idle like its a damn Harley at any temp, only other symptom is slight miss when accelerating and cruising, random lunges on decel.
                    sigpic
                    1991 325i Sport - Calypsorot Metallic - DAILY DRIVEN

                    WTB in SoCal: 8"/10" Lukebox, leather Sport steering wheel, 60L MotoMeter fuel gauge, Thule/Yakima roof rack

                    Comment


                      #11
                      Yes, I'm almost certain there is an issue during closed loop only. I will report back once I've investigated further.
                      90 325i DD/Track
                      03 Durango 5.9


                      Originally posted by e30mpg
                      It is recommended to get new gasket but this is R3v and we just copper spray that shit......slap biotch on and tighten to tq.

                      Comment


                        #12
                        It has been said, but I would look at that o2 sensor again, and o2 sensor relay at the left front strut.

                        Comment


                          #13
                          Temp sensor registered at ~1800 ohms cold and ~230 warm. Those are lower than expected, but the rate of change is somewhat accurate. I swapped it anyway, no change in idle.

                          O2 test at 0.012v at idle and 0.15v at 3,000 RPM. The 0.15v reading was peak, not constant. The constant voltage at higher RPM was more in the 0.03v range. I pulled an O2 from a yard yesterday and will test today.

                          I already swapped the relay, no affect.
                          90 325i DD/Track
                          03 Durango 5.9


                          Originally posted by e30mpg
                          It is recommended to get new gasket but this is R3v and we just copper spray that shit......slap biotch on and tighten to tq.

                          Comment


                            #14
                            Does the O2 do anything during cold idle?
                            90 325i DD/Track
                            03 Durango 5.9


                            Originally posted by e30mpg
                            It is recommended to get new gasket but this is R3v and we just copper spray that shit......slap biotch on and tighten to tq.

                            Comment


                              #15
                              Well, the threads on the junkyard O2 were just bad enough that it won't go it and I don't want to force it. Hopefully pick up another O2 tomorrow.

                              Going to look up the process for testing the TPS and try that as well.
                              90 325i DD/Track
                              03 Durango 5.9


                              Originally posted by e30mpg
                              It is recommended to get new gasket but this is R3v and we just copper spray that shit......slap biotch on and tighten to tq.

                              Comment

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