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HT4100 4.1, 4.5, 4.9 Discussion, 4.9 Will Not Idle Below 2500rpm! in Cadillac Engine Technical Discussion; Originally Posted by skor The new ISC did fully retract and extend. The throttle switch also worked. After retracting the ...
  1. #31
    HUF's Avatar
    HUF
    HUF is online now Cadillac Owners Connoisseur
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    Re: 4.9 Will Not Idle Below 2500rpm!

    Quote Originally Posted by skor View Post
    The new ISC did fully retract and extend. The throttle switch also worked. After retracting the ISC through the ECM override, I noticed something peculiar. The throttle cam was not on the min air screw even though the ISC plunger screw was turned in as far in as it would go.

    At this point, I removed the ISC plunger screw from the new ISC plunger and compared it to the screw from the old ISC motor. The plunger screw on the new motor was significantly longer than the screw on the old ISC motor. I installed the old ISC plunger screw in the new motor, did the adjustment and idle relearn, and all is now well.
    LOL Happened to me too! While adjusting new ISC motor I noticed the plunger would not go in far enough. So I unscrewed it and compared to one from old motor. It was noticably longer. I cut it off and that was it. I thought at the time the motor was not exactly for my car...

  2. #32
    peteski is offline Cadillac Owners Enthusiast
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    Re: 4.9 Will Not Idle Below 2500rpm!

    Ah, thanks for the explanation skor.

    Now it all makes sense. When adjusting for min idle the ISC plunger is not supposed to be touching the throttle cam. But I suppose that you've done the adjustment with the old ISC and then you didn't check again after installing the new ISC.

    Peteski

  3. #33
    skor is offline Cadillac Owners Member
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    Re: 4.9 Will Not Idle Below 2500rpm!

    Quote Originally Posted by peteski View Post
    Ah, thanks for the explanation skor.

    Now it all makes sense. When adjusting for min idle the ISC plunger is not supposed to be touching the throttle cam. But I suppose that you've done the adjustment with the old ISC and then you didn't check again after installing the new ISC.

    Peteski
    Try this. Use the ECM override to retract the ISC motor as far as it will go, then disconnect the ISC motor. After the ISC is disconnected from the wiring harness, apply 12 volts to the the blue wires on the ISC motor. You can get the ISC motor plunger to retract further in until it bottoms out. This is how the motor came out of the box and in was in this possition that I did the initial adjustment.

  4. #34
    peteski is offline Cadillac Owners Enthusiast
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    Re: 4.9 Will Not Idle Below 2500rpm!

    Interesting. IIRC, mine retracts all the way in (and it sounds like it is ratcheting). But I have 85 Eldo with a 4.1 engine. Although I'm pretty sure that the ISC is the same. But the ECM is different.

    Peteski

  5. #35
    n2prise is offline Cadillac Owners Member
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    Re: 4.9 Will Not Idle Below 2500rpm!

    I read all these posts and I have something else to add. I have a 96 Deville with occasional idle problems. Half the time that this occurs, the air conditioning compressor goes off line and no cool air of course. I pull off the road, turn everything off. Sometimes this is all it needs. I feel like the car is running Windows XP with bugs or something. I run a diagnostic and get no codes. That is why the ISC motor thing caught my attention.

    Any explanation why the AC compressor goes off at the same time the idle goes high? I have seen 3500 RPM with the transmission in neutral or park. ON the freeway, it is like the cruise control is set to 75 or 80 MPH.

    I look forward to hearing any ideas.

    Thanks!

  6. #36
    snydly402 is offline Cadillac Owners Member
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    Re: 4.9 Will Not Idle Below 2500rpm!

    kdcing, do you know how to do that with the 4.5 because the book is worthless on how to do the learns tps instructions and the codes on overriding the pcm to retract the isc motor.

  7. #37
    kdcing is offline Cadillac Owners Fanatic
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    Re: 4.9 Will Not Idle Below 2500rpm!

    ...don't know the 4.5, however, you can probably follow the manual process to have the ISC's plunger retract. That is,

    1. Start engine and get under the hood.

    2. With 1 hand, open the throttle slightly to 2k engine rpm or higher. The ISC plunger should begin to retract.

    3. Once the ISC is fully retracted, use your 2nd and 3rd hand to disconnect the ISC at its pigtail/connector.

    The following may work to do the relearn:
    1. Find the idle screw and turn out to reduce engine speed to 425rpm or less (yep, the engine will stumble and putter and just about die).

    2. Disconnect the battery for some time to clear the computer memory. If I recall correctly, 30 seconds is sufficient....better yet, leave it disconnected for 5 minutes.

    3. Reconnect the battery and ISC. Start the engine. Run engine in Park for 2 minutes, then in drive (w/ foot on brake) for 2 minutes.
    This procedure is taken from memory and may or may not be accurate.

  8. #38
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    Question High or erractic idle on my 4.9

    I realize this is an old thread, but I just read the entire thread and copied 6 pages of stuff from all you Cadillac experts and will keep these notes handy just in case.

    My 93 Seville 4.9 sometimes (not all the time) idles pretty high (never as high as 2,500 though!) but it comes back down after a few minutes. I park my car in a dry, relatively warm garage (has a furnace vent going into it but of course that's worthless with gaps in the overhead door!). It never gets below about 45-50 degrees in my garage, so it's not like my sensors are "thinking" it's an icey morning.

    Sometimes when I start it, it goes up pretty high, like close to 2,000 but slowly goes down, yet sometimes is stays above 1,000 and feels like I'm getting ready to do a big power brake smoke show in a RWD hot rod. I attempt to "kick it down" (just a habit from my carb engine days) to no avail. But eventually it will go down.

    Another thing my car does (but only when it decides it wants to, NOT all the time) is when I start it, it will start and die, start and die, start and die... until I give it a little gas pedal and start it then it sounds like it's missing for a minute (like old cars when they were flooded) and eventually clears out and runs fine. Once in awhile, after it does this, it will start fine but the RPM's go up and down drastically like 500 to 1500 and back and forth a few times like it wants to die. I'm sure there's a name for this, but I'll just call it stumbling or erratic idle.

    Since the higher RPM idle only lasts a matter of minutes, I'm not too concerned about it yet. But the up & down idle and sometimes starting and instantly dying is driving me crazy!!!

    I keep thinking it's related to the TPS but not sure, since Cadillacs seem to have like several thousand sensors and plugs and wires and harnesses and like 150 fuses under the hood! (Slight exaggeration).

    Any suggestions would be greatly appreciated. This is my first Cadillac and I've only had it 2 weeks so I'm still learning things.

    BTW, I do have a DMM if there are any tests I can do with it.

  9. #39
    the recluse is offline Cadillac Owners Connoisseur
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    Re: 4.9 Will Not Idle Below 2500rpm!

    Three things; either MAP sensor, TPS sensor, or ISC needs adjustment.

    Go to the Eldorado/Seville section and look under the sticky on how to pull codes. Follow the instructions and post back.

  10. #40
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    Re: 4.9 Will Not Idle Below 2500rpm!

    Quote Originally Posted by the recluse View Post
    Three things; either MAP sensor, TPS sensor, or ISC needs adjustment.

    Go to the Eldorado/Seville section and look under the sticky on how to pull codes. Follow the instructions and post back.
    Thanks.

    I hope I didn't confuse anyone will all the things my car is doing or not doing. It's really only 2 things. I just wanted to be as specific as possible to help others offer their advice or opinion.

    Oh, BTW, I copied that procedure last week! I just haven't used it because the only thing showing on my dash is "Low Refrigerant Level, A/C Pump Disabled". But I can pull the codes in the morning and post back. No problem.

    So, it will show a bunch of codes even though the Check Engine light never comes on or the OBD isn't saying anything is wrong? Dang! Guess I better check!

    And I was thinking TPS. But since it only does it "when it wants to" and is not a regular thing, I haven't pulled the codes.

    I'll let ya know! Thanks again!

  11. #41
    drewsdeville is offline Cadillac Owners Master
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    Re: High or erractic idle on my 4.9

    Quote Originally Posted by Hairball View Post

    Another thing my car does (but only when it decides it wants to, NOT all the time) is when I start it, it will start and die, start and die, start and die... until I give it a little gas pedal and start it then it sounds like it's missing for a minute (like old cars when they were flooded) and eventually clears out and runs fine. Once in awhile, after it does this, it will start fine but the RPM's go up and down drastically like 500 to 1500 and back and forth a few times like it wants to die. I'm sure there's a name for this, but I'll just call it stumbling or erratic idle.
    .
    This right here is a classic by-the-book leaking fuel pressure regulator symptom. When the car is shut down, the residual fuel pressure is bled off into the intake manifold through the leaking diaphragm, causing hard flooded starts.

    This could also be whats causing the random fast idle. The computer has learned the idle with the hard starting problem. As the engine initially chugs, like you say it does, the pcm calls for more throttle to bump the idle up. When it clears out the idle ends up being too high and it has to dial it back.

  12. #42
    the recluse is offline Cadillac Owners Connoisseur
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    Re: High or erractic idle on my 4.9

    Quote Originally Posted by drewsdeville View Post
    This right here is a classic by-the-book leaking fuel pressure regulator symptom.
    Good eye. That's about $40 and an hour to swap out.

  13. #43
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    Re: High or erractic idle on my 4.9

    Quote Originally Posted by drewsdeville View Post
    This right here is a classic by-the-book leaking fuel pressure regulator symptom. When the car is shut down, the residual fuel pressure is bled off into the intake manifold through the leaking diaphragm, causing hard flooded starts.

    This could also be whats causing the random fast idle. The computer has learned the idle with the hard starting problem. As the engine initially chugs, like you say it does, the pcm calls for more throttle to bump the idle up. When it clears out the idle ends up being too high and it has to dial it back.
    Thanks! I'll check that while I'm at it. I sure know one thing: I need to buy a Haynes and a Chilton for this car!!! Can't afford the FSM, but these will help.

  14. #44
    HUF's Avatar
    HUF
    HUF is online now Cadillac Owners Connoisseur
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    Re: 4.9 Will Not Idle Below 2500rpm!

    FSM shipped $25 and MUCH better than a Chilton.
    http://cgi.ebay.com/ebaymotors/1993-...#ht_500wt_1182

  15. #45
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    Re: 4.9 Will Not Idle Below 2500rpm!

    Quote Originally Posted by HUF View Post
    FSM shipped $25 and MUCH better than a Chilton.
    http://cgi.ebay.com/ebaymotors/1993-...#ht_500wt_1182
    SWEET! I'll take one! BUT... it might be a week or so. I'm short on coinage right now but I'm about to get a HUGE check from my parents' estate. When I get it, I'll order one of those! I figured they were like a hundred bucks or more. Didn't realize they were that cheap!

    Thanks so much!

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