Throwing a Diagnostic Code 30 (ISC Circuit Problem)
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RWD 19xx-1984 DeVille and Fleetwood,
1985-1996 Fleetwood and Brougham Forum Discussion, Throwing a Diagnostic Code 30 (ISC Circuit Problem) in Past Cadillac Vehicle Discussion; EDIT: Nevermind... I found the troubleshooting flow chart in my shop manual. :X Sorry, guys. Still getting to know this ...
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    nebulosity's Avatar
    nebulosity is offline Cadillac Owners Fanatic
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    Throwing a Diagnostic Code 30 (ISC Circuit Problem)

    EDIT: Nevermind... I found the troubleshooting flow chart in my shop manual. :X Sorry, guys. Still getting to know this shop manual.

    After starting my engine, I'm getting a code 30. Shop manual says there is a problem the ISC circuit? Sounds kind of vague. Where do I start to try to fix the issue? o_O Any ideas?

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    SafariOne is offline Cadillac Owners Fanatic
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    Re: Throwing a Diagnostic Code 30 (ISC Circuit Problem)

    Trying to work on that one myself as well. It is tied into the TPS circuit and one can trigger the others code. Do you get any throttle ratchet on the gas peddle?? Could be the throttle switch which is part of the motor.assembly. If the throttle lever is touching the ISC adj. bolt at idle then the code will throw. You have to go through a bunch of switch tests to get to the root cause. Shut the engine down and wait at least ten seconds and then turn the key on and see if the ISC extends...air cleaner off of course.
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    nebulosity's Avatar
    nebulosity is offline Cadillac Owners Fanatic
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    Re: Throwing a Diagnostic Code 30 (ISC Circuit Problem)

    Quote Originally Posted by SafariOne View Post
    Trying to work on that one myself as well. It is tied into the TPS circuit and one can trigger the others code. Do you get any throttle ratchet on the gas peddle?? Could be the throttle switch which is part of the motor.assembly. If the throttle lever is touching the ISC adj. bolt at idle then the code will throw. You have to go through a bunch of switch tests to get to the root cause. Shut the engine down and wait at least ten seconds and then turn the key on and see if the ISC extends...air cleaner off of course.
    It turns out that I got the code to clear after fiddling with the throttle linkage -- I'm not entirely sure what fixed it, but we took up a little slack and played with the ISC motor plunger a little. On the following start up, the 30 code didn't come back. o_O

    Now I have to figure out why my "service soon" and "service now" engine lights are coming on while the engine is running and the ECM shows no codes. o_O

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