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Thread: Idle issues

  1. #1
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    Idle issues

    I've been fiddling with an idle problem for awhile now and hoped to get it solved, but here I am. Typically idles high. When I start the car it's about 1000 rpm and when it warms up after a few minutes goes to 14-1500 rpm. I backed off the microswitch and idle screw but it stayed at high idle. I also checked the microswitch to ground and it is working properly.

    I disconnected inner bulkhead on ECU and it goes to 2500. Unplugging the outer does not change anything. I tested the thermistor on the 4 pin bulkhead at the ECU and found resistance so assumed it's working. I also swapped it with another ECU I have that is known good and had the same results.

    I checked around injectors and vacuum lines with carb fluid but didn't spot any leaks.
    I checked the idle motor and it does hum. Also, just for good measure took it out and sprayed carb fluid in it and shook it around a bit. At one point I checked voltages on the idle motor connector and noticed 12 volts center pin, about 10 volts to one side but 0 volts to the other. I assumed that it was just not signaling one side at the time. The Lambda system does buzz.

    I tested the Lambda Dwell with the engine warmed and the O2 sensor disconnected and got 44. (Using Orange wire and ground on the engine ground on the intake 4 cylinder mode)
    The engine idles around 850 rpm with O2 sensor disconnected.

    When I connect the O2 sensor the idle goes up to 14-1500 rpm and here's the disturbing part. The Dwell goes to about 84. I messed a bit with the air/fuel screw on the distributor and I can get the RPMs to drop to 800 but it smells like it's running to rich and wants to flood so I put it back the way it was. Also, that didn't seem to change the Dwell with the O2 sensor hooked up and I understand that it should be around 40, not 84.

    In any case, the Lambda system is working very hard when the O2 sensor is hooked up.
    Questions:
    1.) Could a bad O2 sensor cause this because it does seem to be working.
    2.) I didn't check continuity on all ECU lines, but unhooking it didn't seem to matter. I did consider that the motor might just stay in the state it was left in, and perhaps if one side's not working
    3.) Any other ideas based on what I've done so far?

  2. #2
    Senior Member Bitsyncmaster's Avatar
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    If your getting vacuum advance at idle, you will be about 500 RPM to high. So I would test you have no advance by pulling the hose off the ignition distributor.

    You do not use the mixture screw to set idle speed or idle smoothness. Set it with your meter and fix other problems when set correctly.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  3. #3
    Member
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    Quote Originally Posted by Bitsyncmaster View Post
    If your getting vacuum advance at idle, you will be about 500 RPM to high. So I would test you have no advance by pulling the hose off the ignition distributor.

    You do not use the mixture screw to set idle speed or idle smoothness. Set it with your meter and fix other problems when set correctly.
    Thanks for the reply. With the car warmed up I can remove one or both vacuum hoses to the vacuum solenoid (one of which goes to the distributor) and it doesn't change the idle.

    I did notice when I start my car from dead cold it idles at about 775 for a few minutes, then once it warms up jumps up to 14-1500 rpm. If it's already partially warmed up it will idle at 1000 for a minute or so then go to 14-1500, that part seems to depend on how warm it is.

  4. #4
    One of those purists you keep hearing about. sdg3205's Avatar
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    Dale, check your three bank enrichment screws on the butterfly assembly are in tight. I had dwell issues and these were all just loose enough to cause issues.
    Dave

    Here, somewhere.


  5. #5
    Senior Member Bitsyncmaster's Avatar
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    Your engine takes more throttle (idle motor opens more) when the engine is cold. That is due to the oil being "thick" and other tighter tolerances.

    Since your holding the 775 RPM cold that tells me your idle system is working but must be running out of it's control range as the engine heats up.

    Try backing off the curb idle screw (lower screw on throttle arm) which also may need the idle switch screw to be backed off if it bottoms out on the idle switch.

    If you find like I did that even with that curb idle screw backed all the way out the idle would still climb after the engine warmed up, you may have the bad deceleration springs like I had. Once I replaced the throttle assembly that fixed my high idle.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  6. #6
    Senior Member DMCFL Brandon's Avatar
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    Quote Originally Posted by Bitsyncmaster View Post
    Your engine takes more throttle (idle motor opens more) when the engine is cold. That is due to the oil being "thick" and other tighter tolerances.

    Since your holding the 775 RPM cold that tells me your idle system is working but must be running out of it's control range as the engine heats up.

    Try backing off the curb idle screw (lower screw on throttle arm) which also may need the idle switch screw to be backed off if it bottoms out on the idle switch.

    If you find like I did that even with that curb idle screw backed all the way out the idle would still climb after the engine warmed up, you may have the bad deceleration springs like I had. Once I replaced the throttle assembly that fixed my high idle.
    I had the same issue. I changed out my throttle butterflies with soft decel springs with newer, stronger ones and my idle went back to normal.
    Brandon S.

    2014 Honda Civic EX
    2016 Toyota Tacoma SR5 V6


  7. #7
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    Quote Originally Posted by sdg3205 View Post
    Dale, check your three bank enrichment screws on the butterfly assembly are in tight. I had dwell issues and these were all just loose enough to cause issues.
    Dave, Thanks, I did check tightness and sprayed some carb fluid around them, appears no leak.

  8. #8
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    Quote Originally Posted by Bitsyncmaster View Post

    Try backing off the curb idle screw (lower screw on throttle arm) which also may need the idle switch screw to be backed off if it bottoms out on the idle switch.

    If you find like I did that even with that curb idle screw backed all the way out the idle would still climb after the engine warmed up, you may have the bad deceleration springs like I had. Once I replaced the throttle assembly that fixed my high idle.
    OK, I'll turn the throttle screws and look at the deceleration springs this weekend when I can turn a wrench. A quick test this morning before work: Unplugged the O2 sensor and started the motor and let it warm up until fans came on. The idle stayed at 775 rpm and did not waver at any time. Voltage on O2 sensor was 0.09 V when warmed up. Is it possible the O2 sensor is bad or was the idle just staying steady because the lambda system was constant at 45? (It did go to 54 when WOT pressed and idle increased a bit). Your replies help me understand more of how this thing operates and fun to try the tests.
    Last edited by funkstuf; 04-07-2016 at 07:20 PM.

  9. #9
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by funkstuf View Post
    OK, I'll turn the throttle screws and look at the deceleration springs this weekend when I can turn a wrench. A quick test this morning before work: Unplugged the O2 sensor and started the motor and let it warm up until fans came on. The idle stayed at 775 rpm and did not waver at any time. Voltage on O2 sensor was 0.09 V when warmed up. Is it possible the O2 sensor is bad or was the idle just staying steady because the lambda system was constant at 45? (It did go to 54 when WOT pressed and idle increased a bit). Your replies help me understand more of how this thing operates and fun to try the tests.
    You may have not waited long enough but that would suggest your mixture is causing the problem.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  10. #10
    Member
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    Club(s):   (PNDC)

    Quote Originally Posted by Bitsyncmaster View Post
    You may have not waited long enough but that would suggest your mixture is causing the problem.
    But, if I have an air leak somewhere this could still be causing it to be too lean, but the lambda system wouldn't have compensated it when the O2 was disconnected right? I'm going to check again for air leaks. I did spray carb fluid in around where the idle motor pipe goes and didn't detect anything but I never feel like that thing is sealed. I'll also carry out the idle screw tests you suggested this weekend and hopefully come up with some results to report.
    Thanks for all the help here.

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