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Low at idle

This is a discussion on Low at idle within the General Help forums, part of the LSx Technical Help Section category; Hey guys. I been noticing when the car is in gear and I come to a stop the car idles ...

  1. #1
    Senior Member JayTA98's Avatar
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    Low at idle

    Hey guys. I been noticing when the car is in gear and I come to a stop the car idles normally for a few seconds, then the idle slowly drops to the point that i start to get dash vibration. I turn the A/C off is the same. If I turn the A/C on the idle even drops harder for like a second and then it regains. It started before I installed the o2 sensors and the new AD244 alternator. I cleaned the MAF and TB but no luck. I haven't cleaned the IAC yet. I have no SES light. The car has not shut off but it was close one time. I'm going to hook up my scanner tomorrow and check the RPM's. What's the normal RPM with and without A/C on? Any other things that I can check? The car has 115k miles. Thanks.

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    Electrical Engineer KMdef9's Avatar
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    IAC is my guess. Did the same thing in my Jeep. I replaced the sensor, as cleaning it only provided a temporary fix.

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    Senior Member JayTA98's Avatar
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    Quote Originally Posted by KMdef9 View Post
    IAC is my guess. Did the same thing in my Jeep. I replaced the sensor, as cleaning it only provided a temporary fix.
    I see. It will not show a SES light? or is it because is getting stuck?

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    Senior Member JayTA98's Avatar
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    I cleaned the IAC but I don't see any improvement. The IAC moved pretty easy by hand. I will update what i see with the scanner tomorrow.

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    Electrical Engineer KMdef9's Avatar
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    On my Jeep it didn't throw a code. I also couldn't move it by hand, the bad one or the new one, so I don't know if you can movement is good thing.

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    Senior Member JayTA98's Avatar
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    Quote Originally Posted by KMdef9 View Post
    On my Jeep it didn't throw a code. I also couldn't move it by hand, the bad one or the new one, so I don't know if you can movement is good thing.
    hmm. i mean I have to use some force to move it. I will check some more. Thanks.

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    Now in Summit LT1 Flavor! Y2KArcticSS's Avatar
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    Vacuum leaks will do strange things to your idle. The severity depending on the size of the leak. Made my car compensate by idling unusually high, then slowly dipping down below normal and back up.

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    Senior Member JayTA98's Avatar
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    Quote Originally Posted by Y2KArcticSS View Post
    Vacuum leaks will do strange things to your idle. The severity depending on the size of the leak. Made my car compensate by idling unusually high, then slowly dipping down below normal and back up.

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    true that i have to take off some accent i painted in the engine bay area and spray some carb cleaner to see if I find any leak. Thanks for the suggestion.

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    Smiles for 9.5 Years cammed goat's Avatar
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    When you cleaned the IAC, did you look in the hole for any carbon build up?


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    Smiles for 9.5 Years cammed goat's Avatar
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    Another thing, how are your accessories? I only ask because my last car did the same thing one day. Turned out to be a seizing alternator.

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    Senior Member JayTA98's Avatar
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    Quote Originally Posted by cammed goat View Post
    When you cleaned the IAC, did you look in the hole for any carbon build up?
    i did not it was late I will check tomorrow.

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    Senior Member JayTA98's Avatar
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    Quote Originally Posted by cammed goat View Post
    Another thing, how are your accessories? I only ask because my last car did the same thing one day. Turned out to be a seizing alternator.
    simple radio with a small amp. I just bought a brand new AD244 alternator and the volts are fine. It was doing with the OEM alternator as well.

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    Senior Member JayTA98's Avatar
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    Update: I hook up teh scanner and no codes. I checked the live data. It's idling at 650-660 rpms with a/c on or off. In gear it idles at 550 rpm with a/c on or off. There is no change in rpm if i turn the a/c off or on. I noticed that if i turn an electrical load on the rpm drop for a second (i can hear the car vibrate at the dash). I noticed this when i turn on/off the a/c, car lights, or increase the a/c fan speed to max. The voltage doesn't drop while this happens.

    If i touch the accelerator slightly to get the rpm to 700-800 the vibration stops and it sounds like the car is idling normal. if i keep it around 750-800 rpms I can turn any electrical load on and it doesn't affect the car at all. Not sure if it has to do with the new alternator. Is not affecting the voltage. it just makes the dash vibrate when the car idles low.

  14. #14
    Smiles for 9.5 Years cammed goat's Avatar
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    Either you have a defective alternator, or there is a short somewhere. At least to me it sounds this way. How did the alternator wires look?

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    Senior Member JayTA98's Avatar
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    The wires looked good. I replaced the big 3 like 2 years ago with bigger wires. I guess I can put the old alternator back and check. I'm not sure if they will change the alternator if I'm not having a low charge with it. I think if I remember correctly I had this issue even with the old alternator.

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    Senior Member JayTA98's Avatar
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    Well I checked everything again and same thing. I did noticed that when the rpms are low the cab light are slowly dimming on and off. I think this alternator might not work for my car This kinda of sucks because I won't be able to get a refund. I'm going to put the old one back and check if the issue persist. If it doesn't happen with the old one I will return it.

  17. #17
    Senior Member JayTA98's Avatar
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    ok so i put my old alternator back. The idle is alittle lower than usual but is not dropping like with the new alternator. With the old alternator when I turn an electrical load on the RPM don't drop and the cab lights don't surge. The only time the RPMs change is when I turn on the a/c which is normal. I was able to return the alternator and got my money back. Thanks for all the help guys.

  18. #18
    Smiles for 9.5 Years cammed goat's Avatar
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    You might have to get a wire schematic or check the stickies on here and find your grounds and check them over to make sure there aren't any bad ones.

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    Senior Member JayTA98's Avatar
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    it appears the issue worsen when the car is warm. When i start it in the morning and drive around the issue is gone. The more I drive during the day the issue appears. Not sure what to do. I guess I will have to wait until it gets worse and maybe get a better idea of what it is.

  20. #20
    Smiles for 9.5 Years cammed goat's Avatar
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    Maybe I'm wrong, but I am tempted to say you could have a bad/disconnected coolant temp sensor. If it is, your PCM is probably pulling timing as it could be thinking the car is overheating.

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