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Thread: Protege5 Fast Idle Problem, Drops Very Slowly

  1. #1
    Member
    Join Date
    Jul 2010
    Location
    British Columbia

    Protege5 Fast Idle Problem, Drops Very Slowly

    I've developed an idle issue with my stock 2003 Protege5, with manual tranny.


    The idle takes an unusually long time to drop back to normal after revving the engine. If it is running at 3000 rpm for example and I let off the throttle, the idle drops normally until it gets to about 1500 rpm, but from that point on it takes a good 10 or 20 seconds to drop the rest of the way to where it normally idles, about 700 rpm.


    Also, when starting the car in cold conditions, the idle during warm-up is now at around 2200 rpm, whereas normally it would be at 1200 rpm during warm-up.


    Otherwise the car runs normally and has not thrown any related codes. And again, the idle always returns to normal eventually, it just takes way too long to get there.


    Now I have to confuse the issue a bit. Just before this high idle issue started, I had a different idle issue, a very low rough idle together with 2 codes; P0300 "Random/Multiple Cylinder Misfire Detected" and P0401 "EGR Flow Insufficient". I've had a 401 EGR code once before, and cleared it up by cleaning the EGR. So I removed the EGR again, cleaned it, and reset the codes. That was 2 weeks ago and the rough idle issue never came back, and it hasn't thrown any codes since.


    But as soon as the rough idle problem was fixed this fast idle problem started, which makes it seem like the 2 issues are related, but then I can't see how a 300 or 401 code could cause a fast idle. So it could just be a coincidence, and the fast idle issue is completely unrelated to the previous codes.


    I've checked for vacuum leaks, but I can't see that being the problem anyway as the idle always returns to normal eventually. The idle would likely remain high if there was a vacuum leak. But without it throwing any codes I'm at a real loss. Any Ideas would be welcome.
    1990 Miata - Mariner Blue - B.C. Collector Plates
    2003 Protegé5 SE - Sunlight Silver

  2. #2
    Member
    Join Date
    Jul 2010
    Location
    British Columbia
    SOLVED! For the benefit of anyone who comes across this, I thought I'd report what happened.

    It turns out the earlier EGR issue was directly related to the fast idle issue. During that week or so while the car was running poorly due to the bad EGR, the computer tried to compensate for the low idle, probably by adding fuel, or whatever it thought would keep the idle up. What I didn't realize is that the computer will "re-learn" after a while, and this condition of trying to raise the RPM became the "new normal". So even after the EGR was repaired, the computer still thought it needed to compensate, and therefore the idle becme too high.

    As for the fix, this is what I was told by my mechanic: Disconnect the battery and touch the 2 battery cables together for at least 5 minutes. This ensures the power is completely drained from the system, which allows the computer to reset itself. Reconnect the battery. That's it, you're good to go. He said the car may not run perfectly immediately, that some cars take a day or so, or a few on/off cycles to re-learn. In my case it ran perfectly after only 5 minutes.

    Hope this helps...
    1990 Miata - Mariner Blue - B.C. Collector Plates
    2003 Protegé5 SE - Sunlight Silver

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