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    Not quite idling perfectly

    My car idles... a bit rough. On start the car idles like it has a bad intake leak then after a few seconds(2-3) the idle becomes very steady but something's going on that you can feel through the whole car, it's kind of a shake in the idle. Many people don't notice it unless I say something but it is pronounced. You can definitely hear it in the exhaust, and feel it in the cab.
    The engine accelerates jerkishly when cold in lower rpms but runs really well especially when warm, goes 100mph just fine if I want it to. Feels very smooth and doesn't seem to miss or anything when going wide open. MPG is pretty good too I average 25-28.
    I replaced coil, wires, plugs, dist cap, rotor, injectors, timing belt, water pump, crank position sensor, coolant temp sensor, fuel pump, fuel filter, most air hoses, intake boot, valve cover gasket and valve adjustments, o2 sensor, cleaned afm and icv.
    Three oddities I've noticed. If I unplug the AFM the car runs the same as it does without it besides the CEL being on. A local mechanic says he thinks that may be the issue as these e30s use an "average" if its not getting a correct signal from the AFM. Is there a better way to test this than buying a new/used one and swapping? Rarely, if I'm at a stop light, the CEL will go on until I hit the gas which immediately knocks it off. After this happened I decided to do the stomp test, which worked once in about a hundred tries. I did it every time I got to my destination until it worked. Code 1222 Lambda control 1 came out.
    Given all of this information where should I start? Do all of these puzzle pieces come together pointing towards one thing? Analytically I'm thinking the tps might be the issue?

    #2
    Do you have access to a working AFM and ICV that you could swap out? I'd definitely try it as you've covered virtually everything else besides the TPS.
    sigpic2000 323ci
    1987 325is super etta
    1988 M5
    2000 M5
    1989 944 turbo
    1989 325is

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      #3
      I wish. I posted on the meet up section looking for someone in the NE with no luck :(

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        #4
        Hey guys, quick update: no luck switching the afm, the car ran the same way.

        Can anyone pull the plug on their afm and see if it has any effect? I'm suspect that maybe both AFMs are faulty, or perhaps the plug to the ECU is bad.

        I also unplugged the TPS and idled it. The car idled a bit higher this time and perhaps a bit more smooth but still not perfect. I attached pictures before and after? Which is a more correct idle? Do I need to adjust/replace my tps?
        Attached Files

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          #5
          The Lambda fault at idle that goes away when the engine speeds up, the rough cold idle, the hesitation from idle on a cold engine, and the less than smooth idle all suggest intake leaks, possibly aggravated by an aged O2 sensor.

          The O2 sensor is a scheduled maintenance item with a replacement interval of 100k. If that applies, replace the sensor and have a smoke test run (properly) and fix the leaks it reveals.
          The car makes it possible, but the driver makes it happen.
          Jim Levie, Huntsville, AL

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            #6
            New O2 sensor. Would an intake leak at the exhaust gasket manifold cause this behavior? I have new vac hoses, so i think we can count those out. Any home made smoke test remedies? insense?

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              #7
              A leak in the exhaust is not an intake leaks and won't cause the problems you are seeing.

              A smoke test requires a machine, the cheapest of which cost about $1000. So it isn't really a DIY project.
              The car makes it possible, but the driver makes it happen.
              Jim Levie, Huntsville, AL

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                #8
                rough idle

                After days of doing everything you did I got out the carb cleaner and sprayed everywhere. The offending part was a tiny crack in the rubber air intake boot. Hard to find. And the replacement elbow had an extra hole in the bottom for another application so that had to be plugged. 1991 M42. Vacuum leaks are tough. Be persistent.

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                  #9
                  Let me tell you, I went through so much carb cleaner. I sprayed the Throttle gasket all visible hoses etc. Is there anything under all of it that could leak?

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                    #10
                    The complete list of possible causes of an intake leak is:

                    Intake boot
                    Throttle body gasket
                    ICV hoses & connections
                    Brake booster, hoses, and connections
                    Crank case breather hose
                    Evaporative control hoses, valve, and expansion tank
                    Fuel pressure regulator & hose
                    Injector seals
                    Valve cover gaskets & bungs
                    Oil filler cap
                    Dip stick o-rings
                    Oil return tube o-rings

                    While leaks in some of those can be found by inspection or by spraying carb
                    cleaner on suspect areas, not finding leaks that way doesn't eliminate the
                    possibility. Only a smoke test will really work.
                    The car makes it possible, but the driver makes it happen.
                    Jim Levie, Huntsville, AL

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