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93 Civic low idle at operating temperature

Home Forums Stay Dirty Lounge Service and Repair Questions Answered Here 93 Civic low idle at operating temperature

This topic contains 4 replies, has 1 voice, and was last updated by Joseph King Joseph King 2 years, 1 month ago.

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  • #959911
    Joseph King
    Joseph King

    I have a 1993 Civic LX 1.5L that I got for free because it needed a bunch of things done to it. It has 320k miles on it and I just thought it would be interesting to do some of the repairs that it needed on a car that wasn’t my daily driver.

    When I got it, it had a high idle on startup and I adjusted the FICV as described in the videos. Once the car was warmed up though, it would idle really low, sometime like it was going to stall, but it never did. The water pump was leaking so I replaced the timing belt and and water pump as well as the oil pan seal, and crank and camshaft seals. At the same time I replaced the valve cover gasket and the spark plug tube o-rings since they were leaking. Since the car had an old aftermarket distributor cap, I just went ahead and put OEM distributor cap, wires and NGK plugs in the car.

    So the good news is that all the oil leaks appear to be gone and the car seems to run fine except once I drive it 5-10 miles it still idles really low. It never stalls, but it stumbles like it wants to.

    I followed the idle relearn procedure in the Honda manual and I can’t seem to get it to idle at the proscribed rpms with the IACV unplugged so that made me think that something was going on outside the IACV.

    To try to diagnose the issue I have tried the following:
    Re-bled the coolant
    Check for vacuum leaks
    ECU reset
    Idle relearn
    Checked the TPS voltage
    Checked the timing
    Checked the components of the distributor
    Checked the fuel injectors
    IACV opens when 12v applied

    Oil pan seal (Fel-pro), Cam/crankshaft seals (Fel-pro), Valve cover gasket (Fel-pro), Tube o-rings (Honda)
    Exhaust (except the catalytic converter)
    Spark plugs (NGK), wires (Denso), distributor cap/rotor (Honda)
    Timing belt (Gates), belt tensioner, water pump (Aisin)
    Fuel filter

    Based on Eric’s recommendations I see that he suggests maybe replacing the aftermarket PCV with an OEM. I could also, check the timing belt tension again, but I followed his video and it seemed like I had it tensioned correctly. I also considered the fuel pump, but wasn’t sure that would only be a problem when the car was warm.

    I’m just looking for some ideas of next steps without dropping money on parts. I have the Honda manual and have gone through the flow charts for idle problems and it seems to point to the IACV or ECU (Flow charts end in “try a known good”), but I was hoping to have a better sense that this was the problem before buying those parts.

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  • #959946
    Joseph King
    Joseph King

    One thing that I failed to mention is that I did pull off the IACV and clean out the screen and inspect the throttle body, but neither had anything significant clogging them.

    Joseph King
    Joseph King

    A couple other notes.

    * Tapping on the IACV has no effect
    * This thread seems relevant:

    I see Eric recommended replacing the PCV with an OEM and to check the idle so I will probably do that first.

    • This reply was modified 2 years, 1 month ago by Joseph King Joseph King.
    Joseph King
    Joseph King

    Did a couple things today:

    * The coolant temperature sensor is reading 210 ohms (200-400 is normal)
    * The air temperature sensor is reading 550 ohms (.4-4k is normal)
    * I replaced the PCV and did an idle relearn with no noticeable effect

    Joseph King
    Joseph King

    I created a video that shows the behavior. At about 15 seconds, the fan kicks in and the idle rises, but once the fan cuts off around 40 seconds you can hear the idle drop.

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