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Unread 05-15-2008, 05:53 PM   #1
SyntheticShield
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High Idle Speed

Got a problem with my wifes Jeep Cherokee. She stated that when she drove it this afternoon it was idling very high like someone had there foot on the accelerator and then at times it seemed like it didn't want to shift.

When I got home I started it up and its definitely idling high, I don't know how high because it doesn't have a tach, but I would say 1500 rpm or higher. I don't hear any vacuum leaks, but I checked all the lines I could and didn't see anything obvious.

I'm not real sure what else to check. I cleaned the IAC (Idle Air Control sensor), but I don't have anything thing to check and see whether it is bad or not. The accelerator is not stuck or anything like that.

Anyone have any ideas where I can start or what to check. I dont want to replace parts in the blind as I imagine that could get costly in a hurry. Thanks in advance for any assistance.

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Unread 05-15-2008, 05:58 PM   #2
SyntheticShield
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I thought I would add that there is not a check engine light, but I may hook up my scan tool just the same and see if anything stands out if it will work on the Jeep. I have AutoTap 1-2-3 which is supposed to work across the board but I have had problems in the past scanning Dodge vehicles, so we'll see.
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Unread 05-16-2008, 02:15 AM   #3
balloo93
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Pop the hood remove the TB tube and fire it up. See if you can manually seat the Throttle arm down more (shutting the butterfly). If you can then clean the inside of the TB to remove Crabon build up and lube the throttle return spring and make sure it has plenty of tension on it.

You can check the MAP and make sure the connection is perfectly tight at the TB.

Your IAC motor may be bad. It will open up a bit more at start up and close a little and drop idle after it as ran a bit.
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Unread 05-16-2008, 05:34 AM   #4
SyntheticShield
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Thanks for the reply balloo. I have already done as you mentioned, tried shutting the throttle body butterfly, and that had no effect. I went as far as to disconnect the MAP sensor to see if it would change anything and it did, so the MAP sensor seems to be working. When the MAP was removed it seemed to go to the other extreme and idled just barely high enough to keep it from stalling.

I was thinking that perhaps the IAC was bad, Id just love to be able to prove it so I am not taking shots in the dark. I guess I could hook it up to a 12v source and see if the plunger moves.

Anyway, thanks for your reply and input. If anyone has any other suggestions, please post up. Thanks.
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Unread 05-16-2008, 06:50 AM   #5
balloo93
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I think it uses a 5v supply.
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Unread 05-16-2008, 09:51 AM   #6
oldmanscherokee
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unplug the tps sensor on the throttle body, if it drops theres your culprit
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Unread 05-16-2008, 07:24 PM   #7
SyntheticShield
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Thanks for the replies everyone. Well I went ahead and bought a new IAC feeling confident that that was the issue, but once replaced the high idle speed remains.

oldmanscherokee, I pulled the connector off the TPS as well and the high idle speed remains.

I pulled off the throttle body and cleaned it inside and out, cleaned the IAC port, got all the carbon build up out and everything. Sprayed some copper spray on the TB gasket just in case there was an issue there and re-installed everything, high idle speed remains.

Im not sure what else to check. I looked at all the vacuum lines I could find, they mainly seem to run along the firewall so I just followed them around to wherever they went. None are worn, have any worn spots in them, all the connections are good. Im just plain out of ideas right now.

The only thing that has made a difference in the idle speed has been when I pulled the map sensor completely off and then it seemed to idle too low near stalling. I can put the jeep in drive, reverse and the idle speed drops but you can tell its pulling on you a bit and it acts intermittently when I do that like it wants to stall all together.

If anyone has any other ideas I would love to hear them. My wife is without a ride right now and cant drive my vehicle because she doesnt know how to drive a manual transmission.
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Unread 05-16-2008, 08:09 PM   #8
SyntheticShield
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Okay, good news I think. I hooked up my scan tool, like I probably should have in the first place and discovered a few things.

1. Apparently my Check Engine Light does not work, I found two codes stored. The first was 7E which translates to P0138 as best I can tell and states O2 Sensor 1/2 voltage high or shorted to power. The second was 9D which translates to P1391 as best I can tell and is loss of cam or crank signal or No Crank Reference Signal/Intermittent Loss Of CMP Or CKP. So I got some sensors to replace it would seem

2. The TPS does indeed appear to be bad. oldmanscherokee, I promise you I took off the connector and nothing changed and I even did it again just now and it does not change the idle speed.

While I had the scan tool connected setting up all the parameters to read, I had the engine running and out of the blue the idle speed comes down. Comes down to around 800 rpm and goes from there back up to over 1000 to as high as 1600. Once it settled down, it would still idle just a couple hundred rpm high.

So watching the TPS voltage and Opening percentage I start mashing on the gas and all the sensor reads is between 0.35v and about 0.55v. Throttle opening percentage is fluctuating around just a few percent and I had the throttle open at least 25% if not more.

So I turn off the engine, leave the key in run mode so I can continue to monitor the TPS signal. I mash the gas all the way down and the percentage does not change one bit and it should. So I disconnected the TPS connector and wah lah, I see a TPS voltage of 4.7v and the throttle open percentage jumps to 100% as it should.

So I guess I'll hit up Autozone for a TPS sensor if they have one in stock and let everyone know how that goes.
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Unread 05-17-2008, 06:04 PM   #9
SyntheticShield
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I replaced the TPS today and everything is working as it should again. Idle is normal, shifting is normal. In fact, when we first got the Jeep, when we drove it around and it was warmed up, if you stopped somewhere and put it in park, the idle would dip then restore. It wouldnt stall, just the RPM's would dip briefly then normalize. Well now, its not doing that.

I guess when the wife told me of the difficulty with the shifting that should have clued me in there as I KNOW that to be tied into the TPS. And it has a brand new tranny that has otherwise been running fine. I have fixed other peoples vehicles replacing the TPS when they had trouble shifting. So it should have occurred to me, but I guess I got side tracked with the really high idle speed.

Anyway, thanks for everyones help, I greatly appreciate it.
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Unread 05-19-2008, 10:46 AM   #10
oldmanscherokee
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yeah its not uncommon happens on alot of models not just jeeps. happened to my 1995 lightning and to my jeep thats the only reason i figured id add that in, plus its a simple check, just wierd it didnt drop when you unplugged it
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Unread 06-06-2008, 08:53 PM   #11
Marinerman
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Hi everyone. I've been reading your thread because I have a similar problem. My rpm's are at 1500 when idling. My engine light does work. There is one code coming up - 0720 for a speed sensor which I'll put in tomorrow. But before the engine light came on it was still idling at 1500 rpms. The car's running smooth, just the rpm's are high. Any help would be appreciated.

Forgot - I have a 2000 GC. 6 cyl.

I got lucky. I heard a hiss and couldn't quite pinpoint which hose it was, so I tightened all of them. My idle slowed down to where it should be..about 700 rpms.

Last edited by Marinerman; 06-07-2008 at 07:02 PM..
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