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Romping idle and erratic power antenna

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    Romping idle and erratic power antenna

    Not sure if these two are related. I did an engine swap to a bored/stroked 2.9, and have a few new issues. First is a hard start. Have to crank over a bunch before it gradually catches on and runs. Starts easily when warm, and runs strong on the road. When cold, it seems to idle at normal speed. When warmed up and after throttle goosed, it goes into a romping idle pattern, like a sine wave. Identical to having a bad throttle position switch, including the bucking ride while driving between on/off throttle in first gear. Along with it, the power antenna goes up even with the radio off. Another thing, since the battery was disconnected for a couple of weeks during the swap (I'm slow), the batteries in the dash (for the SIL) died and now my tach and MPG meter are dead. Don't know if that would be a factor.

    At first, I thought it was a simple case of a bad TPS, but unfortunately that's not the case; I've swapped out the idle throttle position switch twice, the idle control valve twice, and even the MAF sensor twice (it has a Miller MAF conversion). No dice. This antenna issue is also new, so I wonder if there's an electrical glitch somewhere as a unifying diagnosis. Any ideas?
    Last edited by Nader393; 11-24-2020, 01:35 PM.
    '91 325i

    #2
    Originally posted by Nader393 View Post
    Not sure if these two are related. I did an engine swap to a bored/stroked 2.9, and have a few new issues. First is a hard start. Have to crank over a bunch before it gradually catches on and runs. Starts easily when warm, and runs strong on the road. When cold, it seems to idle at normal speed. When warmed up and after throttle goosed, it goes into a romping idle pattern, like a sine wave. Identical to having a bad throttle position switch, including the bucking ride while driving between on/off throttle in first gear. Along with it, the power antenna goes up even with the radio off. Another thing, since the battery was disconnected for a couple of weeks during the swap (I'm slow), the batteries in the dash (for the SIL) died and now my tach and MPG meter are dead. Don't know if that would be a factor.

    At first, I thought it was a simple case of a bad TPS, but unfortunately that's not the case; I've swapped out the idle throttle position switch twice, the idle control valve twice, and even the MAF sensor twice (it has a Miller MAF conversion). No dice. This antenna issue is also new, so I wonder if there's an electrical glitch somewhere as a unifying diagnosis. Any ideas?
    Sounds like theres a few different issues happening all at once. I would tackle the easy & obvious ones. Id tackle the SI board first and check the stereo wiring because poorly wired aftermarket headunits will raise the antenna with the ignition on, versus with the power on of the headunit.

    At that point you may notice a few other things along the way. The Miller MAF setup arent the best setups nowadays and they are known to have poor support. Might be time for a Megasquirt upgrade. You like headaches, right?
    Simon
    Current Cars:
    -1966 Lotus Elan
    -1986 Mercedes Benz 2.3-16
    -2006 Volkswagen Jetta TDI

    Make R3V Great Again -2020

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      #3
      Happy turkey day. I got rid of the Miller PSIK (MAF conversion and chip) and went back to the stock airbox and a MarkD chip. It fixed everything. Including the romping idle, weird antenna behavior, and previously dead tachometer and econometer. I don't know how or why the Miller chip accounted for all this, nor how it went bad in the process of the swap, unless it fried when reconnecting the battery power.
      '91 325i

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        #4
        Nice result! 😃
        URL: www.dsylva-tech.ca

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          #5
          Something to be thankful for!

          Simon
          Current Cars:
          -1966 Lotus Elan
          -1986 Mercedes Benz 2.3-16
          -2006 Volkswagen Jetta TDI

          Make R3V Great Again -2020

          Comment

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