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    ECU issue: "erratic idle" condition while driving

    Greetings everyone,

    last week, the CB went under the knife as I redid the rear main seal and oil pan properly, installed the ESP traction bar, and removed one of the double-staked plates, the one with the open IAB's.

    It all went back together earlier this evening, and the car started up fine and had a great idle. Everything was going great until it was time for the test drive. When I started to drive off in first gear, at about 2k rpm's, the ECU starved fuel until the rpm's dropped to normal idle rpm. It continued to do this as I drove, and I eventually figured out that it would do the same thing whenever the rpm's reached that same value near 2k rpm's.

    This behavior reminds me so very much of an erratic idle condition due to a vacuum leak. It is as if the ECU thinks the car is consistently at idle, so that when the rpm's reach a certain level around 2k, the ECU starves fuel to bring the rpm's down.

    My guess, based on these symptoms is that there is either a grounding issue, or the TPS is disconnected. I had one of my students take apart the IM, and I put it all back together myself. I do not recall connecting the TPS when it went back together, so it could very well have been something I forgot. The only strange thing is that no CEL was thrown, and I thought that would happen immediately if the TPS was unplugged. That, however, could be affected by the fact that I am running S300 on a P06.

    What do you all think? I would go check this myself, but that will have to wait until the morning because the car is 30 minutes away. Has anyone experienced this with a bad ground or disconnected TPS?

    Thank you in advance for your help.
    *** Think of others before thinking of yourself. ***
    ********** Spread love, not hate. ***********
    ****Lift others up with kind and helpful words****

    F20A_CB7, I miss you, but I will see you one day.
    "Nothing a little prayer can't fix."


    MRT
    Selling on Ebay!

    15.10 @ 90.42mph
    The quest for 9s ceased, now the goal is a circuit track monster!
    Current fastest Laguna Seca Lap: 1:52.889

    #2
    Something definitely sounds screwy. I've never heard of symptoms like that before!
    If you suspect the ECU, the easiest way to check would be to try a different ECU. Do you still have access to a stock ECU?

    It's very odd that no CEL is being thrown. You're certain the bulb works?

    Aside from the ECU, I would inspect everything you unplugged and messed with when removing that IAB plate. Check all vac lines, make sure all wires are as they should be. Nothing damaged, nothing exposed.

    The TPS is definitely something you need to check, and possibly replace if it's plugged in. That would make sense regarding the fuel starvation, since the ECU wouldn't know that the throttle is opened without that sensor being functional... so it wouldn't adjust fuel delivery. That should throw a CEL, however... of course, the S300 might have something to do with the lack of one. I'm not very familiar with what changes that could introduce.






    Comment


      #3
      That is very weird... Does it hunt for an idle after it hits 2k?

      I don't think a bad ground would cause an issue as specific as this, but anything is possible.

      Also, check your map sensor. I don't remember which throttle body you have, but it's easy enough which ever one you have.

      YouTube Clicky!!

      Comment


        #4
        Thanks guys.

        Deev, I am going to jump the connector and see if a code shows up.

        Sonik, it does hunt for idle every time it hits that value near 2k, just like it would if there was an erratic idle.

        I'm about to go to the car now, plug in the TPS if it is unplugged, reset the ECU, check all grounds, check all hoses into the IM and check the MAP sensor.
        *** Think of others before thinking of yourself. ***
        ********** Spread love, not hate. ***********
        ****Lift others up with kind and helpful words****

        F20A_CB7, I miss you, but I will see you one day.
        "Nothing a little prayer can't fix."


        MRT
        Selling on Ebay!

        15.10 @ 90.42mph
        The quest for 9s ceased, now the goal is a circuit track monster!
        Current fastest Laguna Seca Lap: 1:52.889

        Comment


          #5
          Originally posted by af_1132 View Post
          Deev, I am going to jump the connector and see if a code shows up.
          You said you are using a S300. My S300 gives me the trouble codes in real time. Just plug it in, start datalogging, and click the "Error Codes" tab on the toolbar.

          Comment


            #6
            Guys, the TPS was actually unplugged, haha. I reset the ECU, plugged it back in, and it drove just fine. Now, all I have to do is figure out why only the left side brake light works when all the bulbs are fine, haha.
            *** Think of others before thinking of yourself. ***
            ********** Spread love, not hate. ***********
            ****Lift others up with kind and helpful words****

            F20A_CB7, I miss you, but I will see you one day.
            "Nothing a little prayer can't fix."


            MRT
            Selling on Ebay!

            15.10 @ 90.42mph
            The quest for 9s ceased, now the goal is a circuit track monster!
            Current fastest Laguna Seca Lap: 1:52.889

            Comment


              #7
              well, good thing its fixed
              sold! But here's my build thread for those interested.

              http://www.cb7tuner.com/vbb/showthread.php?t=206864

              Comment


                #8
                Originally posted by af_1132 View Post
                Now, all I have to do is figure out why only the left side brake light works when all the bulbs are fine, haha.
                Most likely the tail light "controller" board on the back of the drivers side tail light. Kinda common for going bad. They go bad in all sorts of ways too.

                Comment


                  #9
                  Originally posted by Mike1357 View Post
                  Most likely the tail light "controller" board on the back of the drivers side tail light. Kinda common for going bad. They go bad in all sorts of ways too.
                  I will have to check that out. All the running lights in the back are just fine, so maybe water leaked in and something shorted out in the board.
                  *** Think of others before thinking of yourself. ***
                  ********** Spread love, not hate. ***********
                  ****Lift others up with kind and helpful words****

                  F20A_CB7, I miss you, but I will see you one day.
                  "Nothing a little prayer can't fix."


                  MRT
                  Selling on Ebay!

                  15.10 @ 90.42mph
                  The quest for 9s ceased, now the goal is a circuit track monster!
                  Current fastest Laguna Seca Lap: 1:52.889

                  Comment

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