Lawrence Look
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Northstar Engines and System Technical Discussion Discussion, Lawrence Look in Cadillac Engine Technical Discussion; hey man its me jim again with that crazy 1993 eldorado, well after driving this thing some more that problem ...
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    1993 eldorado green1's Avatar
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    Unhappy Lawrence Look

    hey man its me jim again with that crazy 1993 eldorado, well after driving this thing some more that problem has came back and sometimes worse, but no codes are present, all are in history, it all started when i tried wot for the first time, now its doing the same idiling real high when im driving, when i stop it doesnt idle down it stays at 3000 but if i kick the throttle real quick it will go down to 1500 then stays at 1200, and the revs are very long, if i tap the throttle even a little bit, she revs way up to like 4000 and stays there for like 3 seconds then slowly comes down, but sometimes it comes down faster, than other, it should be a quick throttle up and down, i never seen this before, its wierd, got anymore advise????

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    Re: Lawrence Look

    IAC valve?

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    Re: Lawrence Look

    That would be my guess Jim, the ISC solenoid. You need to check it while the problem is occuring. If you can close the throttle plate (cam) by hand while running and it slows the idle, it is the ISC motor. Assuming the throttle linkage is not binding.

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    Re: Lawrence Look

    Also pull the 2 vacume lines from the cruise control diaphram and plug them just to make sure its not engaging.

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    Re: Lawrence Look

    Where are you in MI?

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    Re: Lawrence Look

    ok ill try that, tomorrow, the iac is whats controling the high idle though, do u think that code while the engine is running saying i have a bad crank sensor could be the culprit? and im in garden city, about 30 mins west of detroit.

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    Re: Lawrence Look

    Quote Originally Posted by 1993 eldorado green1
    ok ill try that, tomorrow, the iac is whats controling the high idle though,
    Not necessarily, sounds like it is very possible though. The ISC motor pushes against the linkage at the bottom. But first eliminate the easier things. Check that throttle linkage and cable at the throttle body and make sure the cruise control unit is not hanging up.


    Quote Originally Posted by 1993 eldorado green1
    do u think that code while the engine is running saying i have a bad crank sensor could be the culprit?
    I don't think that sensor would make the engine race. Is that code back?


    Quote Originally Posted by 1993 eldorado green1
    and im in garden city, about 30 mins west of detroit.
    I'm in Columbus, if you're down this way bring it by.

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    Re: Lawrence Look

    no current codes, and the throttle assembly moves freely and theres no binding or tightness on any of the cables, lol i dont think in this state its in right now i could drive it anywhere, but i can clearly see the iac making the idle go up and down, but the idle is not really smooth, it seems like the iac has to move alot with only minimal change in idle quality, there is no missing at all, and the only other thing that i notice is the real bad surging when at wot, and it sometimes slams itself into second gear, never used to do that neither, ima gonna go check codes right now and see if it has any, ill write back in a min.

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    Re: Lawrence Look

    ok with key on and engine off theres no current codes, accept the ac and air bag, with the car running i get the same ones plus p083 witch is crank sensor to ignition failure, i dont know im stumped,

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    Re: Lawrence Look

    With the engine idling (too fast), push real hard on the throttle cam (trying to close the throttle plate). To see if you can slow the idle. Does the idle slow down?

    Then disconnect the wire from ISC motor and pull (retract) the ISC plunger back from the throttle linkage. Make sure it's not contacting the throttle linkage. Does this slow the idle?

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    Re: Lawrence Look

    yes, it slows way down, if i physically move it, if i unplug it the engine revs higher and that plunger wont move in.

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    Re: Lawrence Look

    There you go.

    Something is holding the throttle plate open. It should be closed tight when idling, at least until the ISC opens it. Which in your case seems to be opening it too much.

    Likely is the ISC motor, so long as your sure it's not a binding throttle cable, throttle cam, cruise control, or broken throttle return spring.

    Replace the ISC. Might check for a used one, new I think about $140.00.

    After you install the new ISC motor you'll have to do the relearn again.

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    Re: Lawrence Look

    The Cad ISC motor works a little diffeent than say the IAC solenoid on a Honda. The IAC sol allows passage of addtional air "around" the throttle plate to increase speed. The Cad ISC actually opens the throttle plate more to increase speed.

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    Re: Lawrence Look

    yea ill try one on monday but im not gonna get a new one ill go to the junk yard, 140 is a lot for a non returnable part, thanks, ill let you know what happens.

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    Re: Lawrence Look

    Just to be sure, here are some things to check...with the engine idling and in park go under the hood and hold the idle high by opening the throttle lever with your hand. Depress the plunger of the idle speed control motor with your finger and it should retract. Keep it retracting by depressing the plunger firmly until it fully retracts and stops. When it is fully retracted, disconnect the wire connector from the idle speed control motor to freeze it in the fully retracted position. Now, return the throttle lever to the "closed bore" idle position. First thing to check is that there is clearance between the ISC motor plunger and the throttle lever. If it is indeed fully retracted and there is no clearance between the plunger and the lever then adjust the plunger so that there is about .030 clearance. There MUST be clearance between the ISC motor plunger and the throttle level when it is fully retracted. The engine should easily idle down to about 450-500 RPM once there is clearance and the throttle can return to the closed bore setting. If not then determine whether something (like the cruise control link) is holding the throttle open. The cruise control link should have enough slack in it to allow the throttle lever to return to the closed bore position and still have a slight bit of slack. If you adjusted it when working on the engine without returning the throttle lever to the closed bore position it may be too tight. At the closed bore position the throttle lever should be resting against the stop screw that is on the other side of the throttle body behind the TPS. If it is not, then something is holding it open. If it is resting on the stop screw and still is idling too fast then likely there is a vacuum leak from the work you did (assuming that you didn't mess with that screw...) I would then check the intake gaskets one more time and the seal around the perimeter of the intake manifold silver top cover....you didn't need to take that off to remove the intake and the seal may have been damaged around the perimeter of the cover or something. If the engine does idle down fine when the ISC plunger is fully retracted and there is clearance between the plunger and the throttle lever at the closed bore throttle setting then the problem is likely with the idle speed control motor...specifically the closed throttle switch in the ISC motor...that "click" you should feel when you depress the plunger.

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