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Thread: Need Help on Idle Hunting Issue

  1. #1

    Need Help on Idle Hunting Issue

    Short story - I have new injectors, new spark plugs and a new O2 sensor. I've done a vacuum test using a smoke machine and spraying starter flui around and in both cases have not found a vacuum leak. My car hunts at idle when starting cold until it warms up. I try putting a dwell meter on it (after warmed up and after fans and come on and off) and all I get is a reading between 10.5 to 11 when set to 4 cylinder (Half that when set to 8 cylinder). It idles well when warm and I took a short drive and it seems to drive well. Two questions:

    1. What can I check to get rid of the hunting?
    2. Why isn't the dwell meter reading around 40? Perhaps the signal from the O2 sensor not getting trough?

    Shannon

  2. #2
    Banned From "Tight Ship"
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    Cold (<59F) or press WOT switch = 50-60 dwell
    Disconnect O2 sensor => 40-50 dwell
    Disconnect O2 sensor & ground harness lead => 87 or more dwell.
    Disconnected O2 sensor & apply 1.5 V to O2 harness lead => 20 or less dwell
    All readings above should be steady.

    All connected, air cleaner installed, ALL other settings correct and warm engine => 35-45 pulsating dwell
    No longer looking for 5 speed D -- Working on "The other DeLorean" (1966 GTO).

  3. #3
    Here is an update and mostly the news is good. Per the suggestion in the thread, I unplugged my CO2 sensor. The car was running and up to operating temperature with fans cycling. I plugged in the dwell meter. As before, the reading was between 10.5 and 11. I then unplugged the CO2 sensor and the dwell meter reading went up to about 44.7 with little variation. Here is the video of that:
    https://youtu.be/clMgiVDDjhQ
    Whatever adjustment I did on the idle mixture screw did not budge the reading.

    I then plugged the CO2 sensor back in and the dwell meter began fluctuating as it should. I then worked on the tune and here is what I believe is the last video I took:
    https://youtu.be/CMB0WZUy0ao

    The engine actually ran a little bit smoother a couple of days ago when I was unable to get a good reading. If you listen carefully to the video the engine isn't quite smooth but it runs well enough now to drive around. This morning I started the car with a cold engine and it fired up almost immediately. The idle wasn't fluctuating but I would like to smooth it out a little more. I'm not sure if I need to barely tweak the mixture screw or if it's something else.

    Bottom line is that I have a driveable car. I''l probably get a few miles on it and put the meter on it again and make a very slight adjustment.

    Any other tips?

    I took it out for a longer drive yesterday. It hunted a bit when first started. I turned on the AC after a few minutes after it was warm and noticed that the RPM was surging erratically. What's going on?

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