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Thread: Rough and high idle when starting

  1. #1
    Join Date
    Apr 2002
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    Rough and high idle when starting

    I have a slightly rough idle and only when I start my car cold i also have a high idle (goes up to about 2000 rpm) and then when I start moving it'll go back down to normal idle. I've recently replaced the motor mounts, fuel pump and filter, spark plugs and wires. I've heard a lot about the iac going bad? Would this cause the rough idle also? Any input? I'll check my vacuum reading tomorrow. I'm pretty sure its reading pretty normal or slightly off.

  2. #2
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    Mine just started doing this also the last few weeks. When I start cold it wants to die and is rough. Then it gets into a high idle mode for a few minutes until I start driving it. Eventually, it settles down to fairly normal although it seems slower to return to normal idle as I approach a stop.

    I'm suspecting the IAC. Any advice out there?

    Jon

  3. #3
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    Ok i just checked my vacuum and when it starts up it goes to about 18 or 19 and then down to 20 where its supposed to be i believe. I don't really care about the high idle on startup, i just want to lose the roughness. I can feel the car shake side to side sometimes when i'm at a stop light. Anyone?

  4. #4
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    Any ideas?

  5. #5
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    hmm..

    I would also suspect the IAC. My did the exact same thing when mine went bad. Even when it was cold id started up and idled at around 1800-2100 rpm. I had to get a new one from fords because the one's they sell at aftermarket parts stores is "backwards" and they do not work.

  6. #6
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    Anyway to clean it or something? I don't have $100 to spend. Would it produce the rough idle also?

  7. #7
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    Originally posted by derekhay316
    Anyway to clean it or something? I don't have $100 to spend. Would it produce the rough idle also?
    Yup.....actually they recommended that I try cleaning mine first. I think I used carb cleaner, or something of that nature. It did cure the problem for a short while...nevertheless it came back and I had to replace it. Just take it off and clean it with that and a cue-tip is what i used I think. Be careful poking around inside tho.

  8. #8
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    Ok I'll try er out.

  9. #9
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    Exclamation STOP!!!!!



    DON'T CLEAN THE IAC!!

    If it is bad, then it is bad. Just deal with it until you get a new one, but don't clean it out.

    Me and another guy have both had large posts chasing down the problem with an IAC and we both had recently cleaned them out. You'll have nothing but probs after cleaning out the IAC.

    Hope I caught you in time.....

    Edit...Here is link to 6 page post trying to figure out after he cleaned out IAC, My post was longer... http://www.sccoa.com/forums/showthre...&highlight=IAC
    Last edited by BobGPz; 09-15-2003 at 07:58 PM.

  10. #10
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    OK I sprayed some carb cleaner in there so i guess its screwed eh? I guess I'll just have to replace it. Any ideas what would be the cause of the rough idle then? I did a KOER test and came up with code 98: Computer detected hard fault (EEC in FMEM or Failure Management Effects Mode)

    Any ideas?

  11. #11
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    Aug 2002
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    Oakville, Ontario
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    me too

    I need an IAC anybody got one in the toronto area.

  12. #12
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    You may not have screwed it..

    Put it on and see if it is worse than before. May be lucky and it is not the IAC. But these were obviously not made to be cleaned or so many of us wouldn't be having problems with them after cleaning them out. I wonder if the diaphram gets eaten away with the brake/carb cleaner. Hmmm?

    How high is the idle? Any strong fuel smell or anything? Glowing headers? What is your vacuum guage saying at idle and what rpms?

  13. #13
    Yes Bob the cleaner makes the plastic acordian boot hard and brittle, it then just crumbles and falls apart.
    The only thing I would even think about using is Fuel Injection Throttlebody cleaner, its a completely different chemical and is supposed to safe on plastics and electronic sensors.
    Unless the inlet or outlet holes are completely stopped up then do not clean it. There is nothing to be gained by cleaning it internaly.

  14. #14
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    Ok after cleaning out the IAC nothing seems to be different. It still revs up to 2100 rpms when the engine is started any time, and then slowly goes back down and is normal the rest of the time. At idle the boost gauge is at 19 or 18, but when I tap the gas it usually settles down to 20. Could the cause of the rough idle perhaps be the tranny mount? Just one thing i haven't changed while i've owned the car.

  15. #15
    Could the cause of the rough idle perhaps be the tranny mount? Just one thing i haven't changed while i've owned the car.No.

    At idle the boost gauge is at 19 or 18, but when I tap the gas it usually settles down to 20. Sounds like the IAC is lazy in reaction. You probably just need a new one. Those things can fail in several different ways.

    It still revs up to 2100 rpms when the engine is started any time, and then slowly goes back down and is normal the rest of the timeThats what I mean by lazy reaction. The mechanical part of the IAC may be in a bind causing this.

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