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Thread: Extreme high idle?

  1. #1
    Join Date
    Aug 2002
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    Santa Fe (Houston), TX
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    24

    Extreme high idle?

    Hi,

    89 5spd, 185K miles

    I've been reading and searching the forums for some ideas on this problem, but so far no luck. A couple of weeks ago I noticed that the engine was never idling down below around 900 RPM. I've seen high idles before when the IAC bellows was broken, so I took off the IAC and it didn't look bad, but I replaced it anyway. No difference on the idle. Since then, the engine has started revving up, sometimes as high as 2500 RPM and just sitting there. I'm pretty sure the computer is doing it since I can unplug the IAC and the RPMS drop back to normal. The CEL is on all the time, but the only code I get is a SPOUT signal failure (49). I'm pretty sure this is DIS related, but I've had problems with that for a long time and I don't think it's related to the revving problem.

    I'm at a loss here since I'm not getting any codes that seem related. I've been trying to think of why the computer would command the IAC to rev the engine so high. I thought maybe I've got a fuel leak somewhere causing a rich condition and the computer trying to counteract it, but my fuel mileage hasn't really changed much. Also, I would expect the computer to throw a code for a rich condition. Also, it even revs up immediately on startup after it's been sitting a work all day. In that case I wouldn't expect the computer to be even looking at the O2 sensors since they're cold.

    I have 20in vacuum at idle (900 RPM), so I'm not thinking a vacuum leak. I've also put a VM on the TPS and it seems to be OK (around .8 volts closed up to around 4.5-5, nice and smooth).

    One final symptom, the engine fails to start once it's warmed up. Acts like it's flooded. I have to hold the pedal at WOT and get partial starts 5-10 times before it will finally run again. To me that points to a fuel leak somewhere as well.

    Other than the high idle and revving (which is getting more frequent everyday) the engine runs pretty nice. No problems starting after the engine cools down.

    So, any help? I've had the car since about 79K miles and rebuilt the engine once. This is a new one for me!

    Thanks in advance!
    Corbin

  2. #2
    Join Date
    Dec 2002
    Location
    Omaha Nebraska
    Posts
    559

    Iac

    Did you replace the IAC with a new one from Ford? Aftermarket ones won't work (I'm sure anyone else here can explain why). Does the engine make a strange noise? A hooting sound is a good sign the a the IAC has failed.
    At this point, I would think the IAC is also causing your hard starting. Just a hunch. Start with the simple stuff. Have you made any other changes in the engine management lately?
    jj

  3. #3
    Join Date
    Nov 2005
    Location
    Fort Wayne, Indiana
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    2,998
    I am having this same problem with my car to the tee. I gave up and put mine away for the winter. I have replaced the IAC which did not fix the problem and changed out tps sensors although mine checked out just fine. I am getting the spout code as well, also pulled a tps code which I think was related to the high idle problem, not necessarily a tps sensor problem. Check out my thread: http://www.sccoa.com/forums/showthread.php?t=103417

    Notice where I have flucuations of voltage when I use the battery as my ground source versus using the blk/white wire on my sensors? The black/wht wire is the ground source for the sensors. You might want to check that on your car just for point of reference. The same ground source is used for several sensors inlcuding the tps, bap, and various others. My problem is very intermittent, so maybe you'll be able to track yours down easier if yours does it all the time.

    Check a spark plug and see if the problem is causing your car to run rich also.

    I'll fax you wiring schematics if you are willing and capable to check these things. Anything I can help you with just ask, 260-341-2216.

    Chris

    P.S. the no start when hot condition sounds like a different issue. I don't have that problem ever. Oh and the part number for the iac sensor is stamped on it, so you would know if you've got the wrong one.
    Last edited by mywhite89; 11-20-2008 at 09:20 AM.

  4. #4
    Join Date
    Aug 2002
    Location
    Santa Fe (Houston), TX
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    24
    Thanks for the reply!

    I used an aftermarket IAC, but the one that was on there already (and has been for more than 10 years) was an aftermarket part also. And as I stated, I can unplug the IAC and the engine idles back down to almost normal which I assume means that the EEC is actually commanding the IAC to the fast RPMS (in other words the IAC isn't leaking that much). I would agree that the IAC could be causing the engine to never idle below 900, but I don't think that is causing the 2500 RPM idle. The hard starting only occurs when the engine is warm, and I get a lot of black smoke when trying to start it. Again, part of the reason I was thinking flooding of some sort.

    Something occurred to me the morning. Is it possible that the DIS problem is related such that the EEC isn't getting a tach signal and therefore doesn't actually know the RPMS? When I've done the KOER test most recently, I got a 11 (OK) code from the on demand, but I'm always getting a 49 (SPOUT) in the memory codes. My tachometer does work, but I'm wondering if the tach uses a separate signal than the computer does? I know the engine won't run if the DIS doesn't get the crank/cam sensor signals (up shift light, been there), but can the DIS keep the car running if the EEC doesn't get a tach signal? Isn't that what disconnecting the SPOUT plug near the DIS does when you are checking initial timing?

    Just more things to think about!

    Thanks!

  5. #5
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    Nov 2005
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    By pulling the spout plug you disrupt a ground to the computer, magically black/wht wire again. Actual function of how this all works is still a mystery to me.

  6. #6
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    Aug 2002
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    Santa Fe (Houston), TX
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    I wanted to post a correct to my original email. I stated that the Check Engine Light was on all the time, but that was wrong. The Check Gage light is the one that's on all the time. My speedo has been messed up for months, so I assume that the cluster somehow knows there's something wrong. All of the other gauges seem to be OK (other that the gas gauge which is just a pain).

    I played around a little last night, reran KOEO/KOER tests. Still no on demand codes even though the engine seemed to doing it's extremely high idle thing during the KOER test. After clearing the memory codes, I cranked it back up and started unpluging things just to make sure the engine would throw codes. Got everything I expected: MAF, BAP, ECT, ACT, TPS, IAC. I didn't try the O2 sensors (didn't have the car up).

    A little clarification on the hard start problem. It seems to happen only when the engine is warm, but only after it has sat for a while. If I shut the engine off, it will start fine within a couple of minutes (maybe < 5?). But if it sits longer than that, you're pretty much not going to get it to start until she's almost dead cold again. It sat for 45min at work here yesterday morning and when I tried to go somewhere I couldn't get it to start. Again, if I hold the gas pedal all the way down (flood clear), it will hit, but won't stay running. And you can do that over and over again.

    If I had a single injector slowing draining the fuel rail, I wouldn't expect it to keep the engine from starting, just make it upset when it did. I did see a post where someone was talking about the fuel pressure regulator going bad (broken diaphram) and fuel going back up the vacuum line, but I wouldn't think there would be enough fuel in rails to flood the entire engine.

    The engine tend to get a little warm when it's idling at 2500 RPM and I starting to think about just unplugging the IAC until I get it figured out, but I'm worried I'll have decel problems with the 5spd.

    Any ideas would be greatly appreciated!

    Thanks,
    Corbin

  7. #7
    Join Date
    May 2002
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    Quote Originally Posted by choltz View Post
    I wanted to post a correct to my original email. I stated that the Check Engine Light was on all the time, but that was wrong. The Check Gage light is the one that's on all the time. My speedo has been messed up for months, so I assume that the cluster somehow knows there's something wrong. All of the other gauges seem to be OK (other that the gas gauge which is just a pain).

    I played around a little last night, reran KOEO/KOER tests. Still no on demand codes even though the engine seemed to doing it's extremely high idle thing during the KOER test. After clearing the memory codes, I cranked it back up and started unpluging things just to make sure the engine would throw codes. Got everything I expected: MAF, BAP, ECT, ACT, TPS, IAC. I didn't try the O2 sensors (didn't have the car up).

    A little clarification on the hard start problem. It seems to happen only when the engine is warm, but only after it has sat for a while. If I shut the engine off, it will start fine within a couple of minutes (maybe < 5?). But if it sits longer than that, you're pretty much not going to get it to start until she's almost dead cold again. It sat for 45min at work here yesterday morning and when I tried to go somewhere I couldn't get it to start. Again, if I hold the gas pedal all the way down (flood clear), it will hit, but won't stay running. And you can do that over and over again.

    If I had a single injector slowing draining the fuel rail, I wouldn't expect it to keep the engine from starting, just make it upset when it did. I did see a post where someone was talking about the fuel pressure regulator going bad (broken diaphram) and fuel going back up the vacuum line, but I wouldn't think there would be enough fuel in rails to flood the entire engine.

    The engine tend to get a little warm when it's idling at 2500 RPM and I starting to think about just unplugging the IAC until I get it figured out, but I'm worried I'll have decel problems with the 5spd.

    Any ideas would be greatly appreciated!

    Thanks,
    Corbin
    Do the IACs that you tried have a white colored "bellows" like cover inside the end that sits closest to the connector?
    When you traded out the IAC, did you install a new or used one?
    The replacement that you tried, did it have a cable lead?

    The fact that the car idles w/o the IAC makes me wonder if you did something to the throttle plate setting. Throttle plate should be completely closed, but not binding, at the rest position with the cables attached. No gap!

    Lastly, have you done anything at/around any of the intake, especially the IC tubes, recently?

  8. #8
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    Dec 2007
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    Replace the IAC....again.

  9. #9
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    South Jersey
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    With the IAC connector off the car should stall because it should close fully. so it seems to me like you may have a vacuum leak, the iac haas failed and will not close fully or throttle plate will not close fully.

  10. #10
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    >With the IAC connector off the car should stall

    Almost stall - the engine might stumble and then hunt for/settle at a slightly low idle...not stall outright.
    Last edited by KMT; 11-22-2008 at 12:47 AM.

  11. #11
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    Santa Fe (Houston), TX
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    The IAC is the correct one. Everyone keeps saying that I should replace the IAC again, but I don't understand. The EEC knows the RPM of the engine and controls the RPM using the IAC. It's a closed-loop system, right? If the engine is turning too fast, the computer will control the IAC to lower the RPM. I know the computer can control the IAC because it does so during the KOER test and will throw a code if the computer does not see the expected RPM drop. In the case of my problem, the computer is commanding the high RPM for some reason. I'm just trying to figure out why?

    What would cause the EEC to raise the RPM above an idle? My A/C is disconnect, so it's not that. It would obviously raise the RPM to try to keep the engine running if the idle drops too low. But why 2500 RPM?

    Thanks for all the responses!

  12. #12
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    >The IAC is the correct one. Everyone keeps saying that I should replace the IAC again, but I don't understand.

    Seen this msg.?

    Can you upload photos of the new IAC on & off the car?

    >I'm at a loss here since I'm not getting any codes that seem related.

    >...and will throw a code if the computer does not see the expected RPM drop


    What codes have you seen...can you list them all...?

    >My A/C is disconnect, so it's not that.

    Anything else disconnected?
    Last edited by KMT; 11-22-2008 at 12:55 AM.

  13. #13
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    Aug 2002
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    Santa Fe (Houston), TX
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    OK, according to the message you pointed me to, the wrong IAC won't even fit, so how does somebody put the wrong one in? I replaced the original Ford unit with a matching aftermarket one. The one I just put on there was identical as well.

    And, I'll say again that the IAC works just fine during the KOER test. It raises the idle as necessary (including when you do the cylinder balance test which I did and everything passed), and it cuts the idle down to around 700 during the part of the test where it tries to lower the idle. I've been through this already in this thread. I'm certain a bad IAC is not causing the 2500 RPM idle, the computer is commanding the 2500 RPM.

    I'm very glad for all the help, but does anybody have any ideas other than the IAC?

    Thanks,
    Corbin

  14. #14
    Join Date
    Nov 2004
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    Start with the with the basics first before you start thowing money at everything.

    1. Disconnect the battery for 15 minutes or so.

    2. While waiting, take your maf sensor out and clean it up. Use a dab of isopropyl alcohol on a cotton swab and gently clean the elements.

    3. Make sure there is nothing binding up around the throttle cable(s), and that the throttle has full range of movement. The car should be able to idle without the IAC plugged in albeit lower than normal. The throttle plate should actually NOT be fully closed but should have enough of a gap to see light, but you'll have to take the throttle body off to see that. The computer actually has a parameter in it that specifies the amount of air that is getting past the throttle plate.

    4. Check for ANY vacuum leaks....

    Have you added anything to the car mod wise that you haven't told us here?

    Frit

  15. #15
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    Sorry, I got interrupted and forgot to answer the other questions.

    I cleared the codes the other night and drove to work yesterday, and it did do it's screaming-idle thing. Checked the codes and got nothing (11=OK) for both on demand and memory codes.

    The A/C unplugged because the front seal on the compressor is shot and I haven't been able to figure out a way to get the stupid snap ring off the front without the special tool. Nothing else is unplugged.

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