let the thing blow up??
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HT4100 4.1, 4.5, 4.9 Discussion, let the thing blow up?? in Cadillac Engine Technical Discussion; Alrighty. I've read around the forum a little before, a few months back. I know the 4.5's had problems with ...
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    let the thing blow up??

    Alrighty. I've read around the forum a little before, a few months back. I know the 4.5's had problems with a high idle. I was on the highway and it was acting up. When I turn it on sometimes the car idles wildly then drops off. When it does this the check engine light comes on. It acts funny for a little, then works fine. When I went to the dealership the last time, it got some crazy code that they had to call Cadillac about. I guess it was the usual problem that all of these things had. Is there anything I can do at all to minimize this or anything? I don't want to be driving along one day, it does this...then the thing just up and blows up.


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    Re: let the thing blow up??

    Is this yet another one of my posts that everyone knows the answer to but noone responds to? This is prettttty important.

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    Re: let the thing blow up??

    take care of that ISC motor soon you dont want to run it with it like that , causes undue stress from motor mounts to trannys ...get that taken care of SOON ....advance auto had them not to long ago for around 50 bucks , pretty normal failure ont he 4.x cars

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    Re: let the thing blow up??

    ISC Motor? What is it, what does it do and where does it go? I'll get one of those today if I know that that's the problem for real and I know where it goes...

    * thumbs up *

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    Re: let the thing blow up??

    ISC motor controlls the idle by extending a small shaft in and out against the throttle plate cam ...if you have a check engine light push off and warmer and get us some codes to ensure you have a "ISC RPM out of range" code

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    Re: let the thing blow up??

    I lost you with the pushing off and stuff..? lol.

    but yeah, that makes sense. Becasue the car will just randomly speed up and stuff. The pedal jitters around when I'm not doing anything. sometimes it's rather violent.

    I might actually even have a small hole in my flex pipe on the down pipe becasue I noticed that one downpipe bracket rubber hanger is off and it shakes around a bit. But the flex pipe cover mesh stuff is pretty beat on. I'm gonna look at it tomorrow. Does what I'm saying sum up the problem?

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    Re: let the thing blow up??

    Quote Originally Posted by cruella89deville
    I lost you with the pushing off and stuff..? lol.

    but yeah, that makes sense. Becasue the car will just randomly speed up and stuff. The pedal jitters around when I'm not doing anything. sometimes it's rather violent.

    I might actually even have a small hole in my flex pipe on the down pipe becasue I noticed that one downpipe bracket rubber hanger is off and it shakes around a bit. But the flex pipe cover mesh stuff is pretty beat on. I'm gonna look at it tomorrow. Does what I'm saying sum up the problem?
    The ISC (Idle Speed Control) works in conjunction with the TPS (Throttle Position Sensor) and gives feedback to the PCM (Power Control Module).

    All this means is that idle speed is controlled by the computer (PCM) based upon feedback from the throttle position sensor, RPM, and idle speed controller. If the computer has no signal or a confused signal, it will try to compensate, in turn causing a high/low jerky REV imbalance.

    Causes:
    Carbon build up on throttle body and/or EGR tubes
    Throttle position sensor out of range
    Idle speed control not matched to throttle position
    Faulty signal wire/connection
    Computer program error

    I am surprised that your Cadillac dealership did not fix this problem straight off. It is common and an easy fix, especially with the aid of the FSM (Factory Service Manual) plus the dealerhip computer diagnostic equipment.

    To find the defective part you need to run a diagnostic from your onboard CCDIC. You will be checking the throttle position sensor output and checking the idle speed control according to the procedure outlined in the FSM.

    You may not need to replace anything, maybe just a calibration.

    Typically the whole issue is caused by carbon building up on the base of the throttle body causing the throttle blade to either bind and/or not fully seat when closed. The first signs of this happening are poor fuel economy and lackluster performance.

    Normally the first steps are to disconnect the negative battery cable, clean the EGR tubes (beneath the throttle body), clean the throttle body and blade, reconnect the negative battery cable, and test for proper opertation.

    Run a search "clean EGR tubes" in the 4.X section of this forum for a how2.

    If the cleaning makes no difference at all, you will need to run a diagnostic to see if the throttle position sensor is within range and calibrated to the idle speed control.

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    Re: let the thing blow up??

    I already cleaned that off before. That was one of my first attempts. The throttle body is fine and the performance is quite surprising. But no, it wasn't a Cadillac dealership. It was a Chevy dealership that we always go to. They saw the code and had to call a Cadillac dealership becasue they didn't know what it was.

    how much more is it to go to an actual Cadillac dealership for service? I don't want to spend all of my money just on shop costs.

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