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Inconsistent high idle problem

Tiny
CHIROKAT74
  • MEMBER
  • 2000 JEEP GRAND CHEROKEE
  • 4.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 211,500 MILES
I have owned this vehicle for about eighteen months and no mechanic has been able to figure out this idle problem. It usually runs high, about 1,000 rpm's in gear and up to 1,400 in park. Sometimes it idles beautifully at 750-800 in gear and occasionally gets as low as 400 but does not shut off. So far I have had the vacuum lines smoked twice (two leaks found first time); replaced the spark plugs, TPS, IAC (twice), PCV, throttle body gasket and computer; and cleaned throttle body. Nothing has worked! The only code I get when the CEL is on is P1294, which is not exactly specific. Any other ideas me or my mechanic can follow up on?
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Thursday, November 22nd, 2018 AT 8:31 AM

13 Replies

Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
Hello, I am Danny,

I have attached a series of pictures for testing your Idle issues. I would have your mechanic check for MAP (Manifold Absolute Pressure) or TPS (Throttle Position Sensor) problems. Hope this helps and thanks for using 2CarPros.
Danny-
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Thursday, November 22nd, 2018 AT 3:41 PM
Tiny
CHIROKAT74
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  • 19 POSTS
I will be sure to pass this along, thanks.
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Friday, November 23rd, 2018 AT 5:48 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,363 POSTS
Hello,

It sounds like you have a bad PCM. I would try a used/rebuilt unit to see what happens here is the location below.

Here is a guide that can help as well:

https://www.2carpros.com/articles/engine-idles-too-high

Check out the diagrams (below). Please let us know what you find. We are interested to see what it is.

Cheers, Ken
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Monday, November 26th, 2018 AT 11:06 AM
Tiny
CHIROKAT74
  • MEMBER
  • 19 POSTS
So the PCM and computer are they not the same thing? The computer (says ECM on the receipt) was one of the first things replaced because that mechanic said all the sensors tested fine. My regular mechanic shop had it all day last week and could not find anything that fixed the problem. He said when they hooked everything back up and tried to do the relearn process that he had to “tap a sensor on the side of the throttle body” to get it to work. They called it an idle sensor, not sure what he is talking about. I gave them the same list of replaced parts that I posted here. Spent a lot of time and money chasing the problem and nothing has worked so far.
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Monday, November 26th, 2018 AT 6:44 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,363 POSTS
Sorry, missed that in the first post. Can you remove the vacuum line to the power brake booster and plug it to see if that makes a difference please? If that does not work lets do a pin to pin test to check for high resistance wires in the throttle control circuits. Here is a guide and the engine wiring diagrams so you can get started:

https://www.2carpros.com/articles/how-to-check-wiring

Check out the diagrams (below). Please run some tests and get back to us.

Cheers, Ken
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Tuesday, November 27th, 2018 AT 11:01 AM
Tiny
CHIROKAT74
  • MEMBER
  • 19 POSTS
That is a good bit over my head, I am afraid, but I actually just asked today about the possibility of an electrical issue since the problem is not constant. I have not been able to leave it with them as it is my only transportation; however, they are going to give me a loaner next week so they can start checking the more in-depth possibilities. I do have a new symptom that may or may not be related; the gas pedal is now sticking in the starting/resting position. This just started when I got it back from the shop last week; they thought maybe they had a clamp sitting in the way from reassembly but all was fine. When it is idling high and I take my foot off the brake, the car will accelerate itself to upwards of 10 mph. Also, the sensor they tapped was apparently the MAP sensor; that is one I actually have not replaced!
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Tuesday, November 27th, 2018 AT 7:35 PM
Tiny
KEN L
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A MAP sensor could definitely cause the issue. Here is its location so you can replace it.
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Wednesday, November 28th, 2018 AT 9:55 AM
Tiny
CHIROKAT74
  • MEMBER
  • 19 POSTS
Okay, definitely going to do that. What is one more sensor! Any relearn procedure or just a straight part swap?
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Wednesday, November 28th, 2018 AT 8:07 PM
Tiny
KEN L
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Should be straight shot but if the computer has taking in false information for a while it might need to be driven to relearn. Let me know.
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Thursday, November 29th, 2018 AT 9:41 AM
Tiny
CHIROKAT74
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  • 19 POSTS
I figured it might take a couple drives for it to register correctly. Think that will have any affect on the gas pedal not wanting to move, or is there something else going on?
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Thursday, November 29th, 2018 AT 5:37 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,363 POSTS
Is this throttle cable or drive by wire?
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Friday, November 30th, 2018 AT 11:27 AM
Tiny
CHIROKAT74
  • MEMBER
  • 19 POSTS
Don’t know what the problem is, just started being stuck in resting position after the mechanic tried to diagnose the idle issue. They thought maybe they had a clamp malpositioned but said that wasn’t it.
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Saturday, December 1st, 2018 AT 11:56 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,363 POSTS
Is this throttle cable or drive by wire? Can you please shoot a quick video with your phone so we can see what is going on? That would be great. You can upload it here with your response.
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Sunday, December 2nd, 2018 AT 10:34 AM

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