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Old 07-01-2015, 12:54 PM
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Low RPM's

My 1989 jeep Cherokee Limited is a rebuild. It has always had a pretty rough idle. But these past 2 weeks has gotten noticeably worse. Without my AC on or my sub connected the RPM is 1000. But with my sub connected it goes down to roughly 750 RPM's when idling. Then when I turn on my AC along with it it shakes below 750 RPM's and dies. So my first thought was the alternator right. So I go to Auto Zone and they test it. Everything comes back clean. Anyone got any other ideas as to what it could be other an a piece of crap?? Haha

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Old 07-01-2015, 01:28 PM
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Re: Low RPM's

Step #1: Post in the correct vehicle and year range forum
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Old 07-01-2015, 01:56 PM
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Re: Low RPM's

When you move the post, provide the engine details and if it was modified/stroked as part of the rebuild. I would presume a sub is a subwoofer, but it would be good to make that clear.

If this is the 4.0, 1000 rpm is a bit high for idle. The idle should go UP when the A/C is turned on...
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Old 07-01-2015, 01:59 PM
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Re: Low RPM's

Quote:
Originally Posted by lstowell View Post
When you move the post, provide the engine details and if it was modified/stroked as part of the rebuild. I would presume a sub is a subwoofer, but it would be good to make that clear.

If this is the 4.0, 1000 rpm is a bit high for idle. The idle should go UP when the A/C is turned on...
I have no idea but the rebuild. It is a 4.0 and yes a subwoofer. And when I got it 1000 rpms was the normal
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Old 07-01-2015, 02:08 PM
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Re: Low RPM's

Get a cheap voltmeter, and measure directly to the battery posts, then turn on the sub and A/C separately and see how much of a drop you get.

Separately, measure across the two posts, then measure from the + to the body right near the battery and see if there is a difference. You could have a bad ground.

That would be the easy stuff, after than you try to pull codes and see if the CPS is having a bad day, O2 sensors, plugged cat...

Wonder why the idle is so high on your 4.0... never hit 1000 even with A/C engaged.
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Old 07-01-2015, 02:09 PM
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Re: Low RPM's

Alright thanks!!
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