'94 Wants to keep on going
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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, '94 Wants to keep on going in Past Cadillac Vehicle Discussion; I'm having a problem with my '94 4.9 70k miles that I hope someone can help with. First symptom: On ...
  1. #1
    Imprl59 is offline Cadillac Owners Fanatic
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    '94 Wants to keep on going

    I'm having a problem with my '94 4.9 70k miles that I hope someone can help with.

    First symptom:
    On startup the engine revs high (like 2500). It quickly drops to around 1200 by the time "Monitored systems ok" goes away and is down to normal idle quickly after that

    Second symptom:
    Upon slowing the car is fighting to keep the engine speed up. If at 40mph I put it in neutral the rpm goes to 1800 and holds there until the speedometer gets to 0. Once the speedometer gets to 0 it drops back to a steady idle at 650.

    I have no codes. I have reset the computer by disconnecting the battery overnight and done the idle relearn per the FSM. Now it is worse than it was before!

    I have checked for vacuum leaks and found nothing. Don't believe it is a vacuum problem since the engine will idle perfectly when the computer will let it. Help??

    Steve B.

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  3. #2
    highonchai's Avatar
    highonchai is offline Cadillac Owners Fanatic
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    Re: '94 Wants to keep on going

    The fighting to stay at speed symptom sounds like something ive experienced. the problem was a seized water pump, the engine simply tried to keep the serpentine belt turning while the water pump was stuck, but shortly after that the belt snapped (as i was pulling out of my driveway for prom, its terrible showing up at prom with a... chevy venture van instead of a cherry Cadillac) Anyway check your alternator water and air pumps for seizure, although if thats the case i cant believe your serpentine belt hasnt snapped yet. Good luck, hope this helps.

  4. #3
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    carnerd is offline Cadillac Owners Fanatic
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    Re: '94 Wants to keep on going

    Ok same thing happend with my caddy.. quick fix. wait till your engine speed has reached the level you want and unplug the ISC (idle speed controler) and your idle will stay at that level all the time. The ISC is the unit that has the bar that pushes on the throttle return. Just unplug it and take a test drive to see how it goes... saves alot of gas!

  5. #4
    BeelzeBob's Avatar
    BeelzeBob is offline I'm a Cadillac Fanatic!
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    Re: '94 Wants to keep on going

    Several things to check and consider.


    First, you might clean the throttle body and make sure that no deposits are hanging the throttle blade open or stopping the air flow to the point that the idle speed control is fighting to keep the engine running and over compensating. Hold the throttle blades wide open and look down the bores. Clean the perimeter of the bores beneath the blades and the backside of the throttle blades. While you are in there, clean the EGR tubes out. Nothing to do with the idle but it will need to be done....one day...anyway. Those two tubes sticking up at you from the bottom of the manifold floor are the EGR tubes and should not be full of carbon. Just rod them out with a piece of stiff wire all the way thru.

    The other thing that could be happening is that the closed throttle switch in the idle speed control motor might be getting weak/intermittant. Hold the throttle open and depress the idle speed control motor plunger...feel the click or detent of the closed throttle switch...or not..??? The closed throttle switch should close or make whenever the throttle is closed. Enter into the onboard diagnostics system with the engine running. Once into the diagnostic mode the icons on the climate control panel stand for the status of certain engine/PCM functions. The OFF icon in specific is the one you want to watch. The OFF icon stands for the status of the closed throttle switch. When you have your foot on the accelerator the OFF icon should not display...i.e...the closed throttle switch will be open. When you release the throttle, the OFF icon should light up as the closed throttle switch should make and the OFF icon would indicate that the PCM is seeing the closed throttle switch close. If the OFF icon tends to agree with the movement of your foot on the accelerator then it is probably operating OK. If, however , when the idle speed control is fighting the engine or the RPM is too high when you are stopping and your foor is off the accelerator and the OFF icon is NOT lit then you may have found the problem. Likely fix is to replace the idle speed control motor although some people have reported success at dissassembling it and cleaning and lubing the closed throttle switch contacts.

    One person had a similar problem (look in the 4.1/4.5/4.9 section of the technical discussions and see the post entitled "surging at idle" or something like that) that turned out to be the torque converter clutch hanging on as the car stopped causing the idle speed control to fight the RPM being dragged down by the locked torque converter not releaseing. That turned out to be the torque converter clutch control solenoid in the transmission pan....

  6. #5
    Imprl59 is offline Cadillac Owners Fanatic
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    Re: '94 Wants to keep on going

    Quote Originally Posted by bbob
    The other thing that could be happening is that the closed throttle switch in the idle speed control motor might be getting weak/intermittant.
    Thanx for the help guys. bbob wins the prize. It is actually the "Lo" lite that comes on instead of "Off" but mine was never coming on indicating that the closed throttle switch was kaput. $70 later I have a new idle speed motor and did the idle learn procedure again. Starts normally now and doesn't idle at 40 anymore.

    Thanx again for the help

    Steve B.

  7. #6
    Big Drate is offline Cadillac Owners Member
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    Question Re: '94 Wants to keep on going

    how come i dont have a tachometer in my 94 deville?

  8. #7
    Imprl59 is offline Cadillac Owners Fanatic
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    Re: '94 Wants to keep on going

    Quote Originally Posted by Big Drate
    how come i dont have a tachometer in my 94 deville?
    It is an option you set within the pcm. Default issue has it turned off for the Deville and turned on for the Eldorado.

    Steve B.

  9. #8
    omarietta is offline Cadillac Owners Member
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    Re: '94 Wants to keep on going

    Quote Originally Posted by Imprl59
    It is an option you set within the pcm. Default issue has it turned off for the Deville and turned on for the Eldorado.
    errrr ... is that easy to do? Or do I need to have it done at the dealership? Along the same line, what about temperatures, can I monitor these too when I'm drinving in any way?

    Thanks.

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