83 4.1 overheated, now, an ISC problem !
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HT4100 4.1, 4.5, 4.9 Discussion, 83 4.1 overheated, now, an ISC problem ! in Cadillac Engine Technical Discussion; Hi, all this is my 1st post, glad to be here except for my problem !! Just bought an 83 ...
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    hendrob is offline Cadillac Owners Fanatic
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    83 4.1 overheated, now, an ISC problem !

    Hi, all this is my 1st post, glad to be here except for my problem !!
    Just bought an 83 Barritz. It had sat for 5 years, but ran. Took it for a 30 mile ride and temp light came on. The engine overheated. Replaced the thermostat and fluid and flushed the rad. Problem cured. HOWEVER when the motor over heated, the engine also reved high at idle. It still continues to do so. The Idle Speed Control extends all the way out and then clicks at the end of its travel,till you accellerate above idle . Can't get the ISC to retract to where is normally was before the engine overheated. ANY info or tips would be appeciated.
    Thanks very much, Bob

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    carnut is offline Cadillac Owners Master
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    Re: 83 4.1 overheated, now, an ISC problem !

    You need to first go into diagnostics and erase all codes, or disconnect the battery to do so. Read the sticky regarding entering and erasing codes on this forum. With the engine running, raise the throttle arm off the ISC. Then while the throttle is held with your right hand, depress the ISC shaft with your left hand. As soon as it is fully depressed, quickly unplug the harness to it. Release the throttle. Now the engine should be idling very, very low. Verify that theres a gap between the ISC and throttle lever. Approx .060 of an inch. If not rotate the end of the shaft with pliers till it is. Now shut off car, wait 10 seconds, reattach the harness to the ISC and restart the car. If you leave the harness attached to the ISC fully retracted, it will short out either the ISC or ECM!! report back.

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    carnut is offline Cadillac Owners Master
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    Re: 83 4.1 overheated, now, an ISC problem !

    Just thought of one other thing. This engine requires the adding of GM sealant whenever the coolant is replaced. Should be a white decal on the radiator support spelling this out. Its VERY IMPORTANT. Failure to add sealant will cause intake gasket failure and/or head gasket failure. Also verify smog pump belt is tight. Found loose, the alternator belt will slip on the water pump pulley and discharge the battery.

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    hendrob is offline Cadillac Owners Fanatic
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    Re: 83 4.1 overheated, now, an ISC problem !

    Hi Carnut, thanks for your assistance. yes I put the sealer in as well. As to the ISC problem, I tried to push the rod back in and it wouldnt go back in the ISC, I checked and reset the codes as you advised. it was showing a 27-open throttle switch signal and a 52 PCM Memory reset, which I dont know what they mean, thanks, regards, Bob

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    hendrob is offline Cadillac Owners Fanatic
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    Re: 83 4.1 overheated, now, an ISC problem !

    Just to add also , a can't see how you can push the rod back into the ISC manually with your finger when it's a gear driven assembly inside . Am I missing something ??
    Thanks, Bob

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    Re: 83 4.1 overheated, now, an ISC problem !

    "open throttle switch" means defective ISC. There is a Throttle Position Sensor on the intake, and a separate Throttle Position Switch that's inside the ISC.

    The E52 "reset" code just means that battery power to the ECM was cut and previous codes were lost.

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    Re: 83 4.1 overheated, now, an ISC problem !

    Hmmmm, I just put a used ISC on from the auto recyclers. It was working fine on the car I removed it from, I had the other car running. However when I put it on my car and started it up, it fully extended causing the car to rev up very high, same as it had done with the previous ISC. This all occured when the car overheated, before that the ISC was working fine

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    carnut is offline Cadillac Owners Master
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    Re: 83 4.1 overheated, now, an ISC problem !

    I've owned 3 4100 cars. Had to adjust every ISC. The factory manual says to do this retracting procedure. I've never had a problem doing this. Yes, you have to keep pressure on the shaft, but it will retract assuming there's power to it. Open can also mean no power to the ISC. An "open" description in car electronics means a disconnected circuit. So blown fuse, cut wire or faulty connector to a sensor would all affect its not working. If the replacement does the same thing then obviously there is a wiring or fuse issue upstream from the ISC.

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    hendrob is offline Cadillac Owners Fanatic
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    Re: 83 4.1 overheated, now, an ISC problem !

    Thanks Carnut, I will try again, when I do push it back slightly, it moves forward again in incriments then "clicks" at the end of travel. I can't figure why it would extend an inch when it over heated so as to cause such high revs.

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    Re: 83 4.1 overheated, now, an ISC problem !

    If it clicks, then its getting power. Thats a good sign. Keep in mind the TPS and ISC work in tandum. dont rule out an open circuit to the TPS.

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    Re: 83 4.1 overheated, now, an ISC problem !

    OK, thanks will check it out. Sorry to sound dumb, but How would a rectify an open TPS circuit ? Thanks !

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    Re: 83 4.1 overheated, now, an ISC problem !

    Just to clarify again, at idle the ISC contiually clicks up apx 3 incriments then snaps back and does the same thing over and over continually until the rpms are increased then it stops until you go back to idle when the process begins again.

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    carnut is offline Cadillac Owners Master
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    Re: 83 4.1 overheated, now, an ISC problem !

    As I said earlier, an open circuit is either a disconnect or cut wire. You need to determine if the TPS is getting voltage or not. Have you retracted the ISC and verified a gap between it and the throttle arm? Is the TPS loose where it attaches to the throttle body?

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    hendrob is offline Cadillac Owners Fanatic
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    Re: 83 4.1 overheated, now, an ISC problem !

    Well the TPS is getting power, it was apx 5.15 volts. As to the ISC I'm about ready to give up I guess, I have tired about everything. BUT soon as you turn the ignition on that ISC STILL tries to push ahead further, even tho it's as far ahead as it can possibly go ! It still clicks trying to go further ahead. I have the screw set in far as it will go just to the car will idle at a decent speed, but of course then the ISC isnt doing a damned thing .
    Im just wondering IF the Computer sent a message to the ISC to speed up when the car overheated on me and it can't clear that message out of the computer ??

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    carnut is offline Cadillac Owners Master
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    Re: 83 4.1 overheated, now, an ISC problem !

    You say you've got the screw in as far as it can go? do you mean the ISC screw or the min. idle screw? Have you pressed the shaft on the ISC to retract it? turning the end of the ISC shaft in results in a very wide gap between it and the throttle shaft. With this wide gap the ISC is trying to extend to close it, hence the ratcheting at the end of its travel.

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