Idle Speed Control
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Cadillac Seville / Cadillac Eldorado Forum Discussion, Idle Speed Control in Past Cadillac Vehicle Discussion; I have been experiencing a problem lately that has me perplexed. The OBD is displaying no codes. My cars starts ...
  1. #1
    Rixky-D is offline Cadillac Owners Member
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    Idle Speed Control

    I have been experiencing a problem lately that has me perplexed. The OBD is displaying no codes.

    My cars starts wonderfully when cold but after warmup starting becomes very poor. It's like you want to press the gas to help get the motor to catch and idle.

    Under the hood when inspecting the area near to the throttle body with a friend to turn the key, the following happens.

    Turn the key on and there is a clicking noise for a second or two coming from the ISC but no movement of any parts. The clicking noise sounds like a worn worm drive clicking over some worn teeth.

    Turn the key off and the same thing happens. The noise is identical but still no movement.

    When starting the motor (cold) there is no perceptible movement from any part of the ISC. The plunger part stays stationary. Nothing seems to move at all.

    I guess I could slightly push on the gas pedal to help start the motor but am not sure this is the answer.

    I am not sure I am even looking at the ISC. Whatever I am looking at, the location is down under the vacuum bellows that I think is for the cruise control and I can see very little of it. I think it is the ISC because there is an adjustable threaded bolt protruding from it and the screw pushes up against the wheel where the cables wind around.

    My first attempt to fix the problem was to thoroughly clean the throttle body and spray with a lubricating cleaner all of the parts that appeared to be moving parts. I also cleaned all of the electrical contacts in the same area thoroughly.

    Should the ISC be making those noises?

    Thanks for reading my post.

    ***

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  3. #2
    Rixky-D is offline Cadillac Owners Member
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    Re: Idle Speed Control

    I finally found a section in the SM that refers to the Idle Speed Control. That SM is really intimidating and involves a lot of re-reading for me to get up enough nerve to perform the tests it indicates to do.

    The first test the SM instructs is to access the OB diagnostics and perform the plunger cycling test P007. It was a positive outcome so now there are additional tests to perform with the motor running.

    The text instructs to select the PCM Overide PS03 and use the dash buttons to perform actions and record the engine rpms.

    Without going into more detail right now my question is this. Do I need to warm up the engine first to do these tests or is it Ok to perform the tests with the engine cold?

    Again, thanks for reading my post. Hope to get a reply.

    ***

  4. #3
    pocketpared is offline Cadillac Owners Fanatic
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    Re: Idle Speed Control

    I can't answer your question but I want to keep this post alive. I just replaced the ISC on my 92 Eldo earlier this year. The car idled all over the place, usually racing up to 1500 - 2500 rpm after startup then during driving. It started perfectly every time, whether hot or cold. Based on my limited experience but relatively thorough researching, it doesn't sound like the ISC is the problem if your car idles fine. I don't think this is bad advice.

  5. #4
    MoistCabbage's Avatar
    MoistCabbage is offline Cadillac Owners 10000+ Posts
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    My guess is that the engine should be at operating temp. Otherwise it would stall when the ISC motor retracts fully.

  6. #5
    basscatt's Avatar
    basscatt is online now Cadillac Owners Master
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    Re: Idle Speed Control

    Do I need to warm up the engine first to do these tests
    or is it Ok to perform the tests with the engine cold?

    engine should be at normal operating temperature

    while you're in there - do all the tests for the TPS - Throttle Position Sensor -

  7. #6
    Rixky-D is offline Cadillac Owners Member
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    Re: Idle Speed Control

    Did all the tests according to the SM and come up smelling like a rose! I guess I'll have to wait until it gets bad enough to throw a code or two. Very disappointing to say the least, it'll probably strand me somewhere away from home! If I could get $2500 for it I'd sell it right now!

    ***

  8. #7
    pocketpared is offline Cadillac Owners Fanatic
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    Re: Idle Speed Control

    Whether starting hot or cold, does the motor settle into a normal idle as soon as it fires?

  9. #8
    Rixky-D is offline Cadillac Owners Member
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    Re: Idle Speed Control

    Quote Originally Posted by pocketpared View Post
    Whether starting hot or cold, does the motor settle into a normal idle as soon as it fires?
    Every time when first starting it up. That's with the motor cold. I'd say half the time otherwise it does settle right away, that's when the motor is warmed up. Some times it stumbles when starting and near want's to stall but it never has stalled at least so far. The remaining few times it just seems to stumble badly, not starting right away but finally does somehow manage to start however roughly.

    I hope I have expressed myself clearly enough to be understood.

    ***

  10. #9
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Idle Speed Control

    Next time it fails to start, press on the accelerator just slightly. If it starts normally, you have found the problem. It's the ISC motor.

  11. #10
    Rixky-D is offline Cadillac Owners Member
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    Re: Idle Speed Control

    Well I'm still experiencing the problem and I can't tell but it seems to be getting harder to start even more. But only when it's warmed up. Cold the car starts perfectly. I attempted to to press the accelerator slightly but that didn't help or seem to make any difference, actually I thought it made it worse but with my anxiety it's hard to tell. Still no codes.
    I can hear the fuel pump working in the tank when I first turn the key on, all the time.
    It scares me cause I feel it will let me down somewhere when I least expect it.
    Thanks for reading my post.

  12. #11
    carnut is offline Cadillac Owners Master
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    Re: Idle Speed Control

    The ISC should be already extended anticipating the next start up. Its extended with the engine cold to provide a faster idle as well. Then retracts as the engine warms. The clicking you hear is most likely a failed ISC. You should see it cycle the threaded shaft in and out as the compressor cycles to carry the extra engine load also. The engine must be up to temp to perform the ISC retracting function. Once fully retracted, pull the connector quickly off of it. Then verify at least .030 air gap between the shaft and the throttle pivot. If no gap or too much gap, screw the shaft in/out to get there. The car should barely run with the shaft retracted. Somewhere around 400 to 500 RPM. If faster than that, then the base idle screw is too far in or the cruise control linkage is adjusted incorrectly. Every time you shut off the warm engine, the ISC shaft should extend, so when you go to restart it the throttle is already depessed. As these cars get older and pass thru other owners, this idle adjustment gets screwed with. As you are finding out this idle adjustment and TPS settings are for better than average technicians and the use of the dash readings in the proper parameters. I use a friend to tell me when the TPS setting is correct sitting in the car, Then I tighten the screws.

  13. #12
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    Re: Idle Speed Control

    Whoa! Wait a minute. I think we all got led down the yellow brick road. You say it starts just fine when cold, but hard starts when it's warm? That sounds suspiciously like a leaky FPR. Pull the vacuum line off the FPR at idle. It's the small canister on the fuel rail. Look for any sign of fuel at the nipple. There should be none. Any sign of fuel means the diaphragm is ruptured and is leaking raw fuel into the manifold. It's like trying to start a warm carbureted engine with the choke engaged.

  14. #13
    eldoradogary is offline Cadillac Owners Fanatic
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    Re: Idle Speed Control

    Quote Originally Posted by Ranger View Post
    Whoa! Wait a minute. I think we all got led down the yellow brick road. You say it starts just fine when cold, but hard starts when it's warm? That sounds suspiciously like a leaky FPR. Pull the vacuum line off the FPR at idle. It's the small canister on the fuel rail. Look for any sign of fuel at the nipple. There should be none. Any sign of fuel means the diaphragm is ruptured and is leaking raw fuel into the manifold. It's like trying to start a warm carbureted engine with the choke engaged.
    I agree with Ranger, also get a gauge and check your fuel pressure. Had the same problem with hard starting when warm on a '92 Eldorado and turned out to be a bad fuel pump.

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