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  • Low Idle Speed Question

    I have a 1995 YJ with the 2.5 - 4cyl engine. It loves the mountains here in Colorado.

    It starts good and runs good, but once it’s warmed up to running temp, the idle speed drops down to 400-500 rpm.

    I’m used to a nice 600-700 rpm. That’s about what it used to be. At 400 rpm it’s too low and doesn’t seem healthy.
    No engine trouble codes.

    I’ve covered the usual tune-up suspects. New: fuel filter, air filter, cap rotor, plugs, and wires. It seems to run good, but none of this has had an effect on the idle speed.

    I’ve cleaned out the throttle body and the idle air control passages. They had some carbon build up, but it wasn’t bad. I replaced the idle air control motor and the throttle position sensor. This has not had much effect with the low idle speed.

    I’ve checked the vacuum lines on the throttle body and intake mainfold for leaks.
    I found one and fixed it, but the engine seemed to idle even lower afterwards!

    I’ve cleaned out the CCV fitting on the valve cover and it’s vacuum line in case that was plugged.
    I finally changed out the oxygen sensor, thinking it might be involved. Even this has not fixed the low idle speed.

    This engine used to idle around 600-700 rpm. At 400-500 rpm it’s too low.

    My Jeep has a case of bad Voodoo!

    Has anyone seen this with their YJ? Any clues what I should check?
    Last edited by MK-101; 02-23-2010, 01:03 AM.

  • #2
    over time the idle adjustment screw tends to wear a little bit causing low idle. sounds like you checked all the other possiable reasons for low idle. try turning the adjustment screw untill you have the rpm you want it at.


    • #3
      Thanks for the suggestion on this! This has been a tough one to sort out.

      I forgot to mention before, that the idle speed seems to have dropped just over the last month or two. My first thought was that it might have been an ignition issue or a bad sensor input to the computer. Not too much left to replace there.

      I’m planning to have a mechanic here scan the engine for things like the: air / fuel, O2, injector signals, and maybe an actual leak-down test on the intake manifold. If anything unusual shows up with that, I’ll post it here.

      If all that comes up clean, I think you may have the fix for me, with the idle stop screw. Thanks for the idea!
      Last edited by MK-101; 02-24-2010, 12:15 AM.