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Unread 05-25-2011, 01:17 PM   #1
Crasher
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1997 ZJ 
 
Join Date: Feb 2008
Location: WI & AZ
Posts: 601
High Speed Idle

My ZJ has been running fine with several starts this spring. However, after sitting for 10 days, The battery was down to just clicking when trying to start. I charged it up and it fired right off as usual except it won't idle back to 800 rpm. It won't come below 1700. I checked for a vacume leak/bad hose and couldn't find anything obvious. The dealer service manager, said the computer could be searching for it's idle setting and that I should drive it for 10 miles or so. I did, but it didn't correct itself. Other than the idle, it runs great and has good power. The check engine light has been on for 2 years, due to a bad CO2 sensor at the cat. I replaced the cat and muffler 2 years ago and did not install the sensor. It's been that way for 7500 miles with no problem, so I'm sure it has nothing to do with the idle problem. Where do I look next?

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Unread 05-25-2011, 01:33 PM   #2
ZJ5point2GCL
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1998 ZJ 
 
Join Date: Oct 2009
Location: Calgary
Posts: 3,392
Bad or really Dirty Idle air valve, just search on here for that or IAC and you'll get more than you ever wanted to know about it.
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Unread 05-25-2011, 05:00 PM   #3
Crasher
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Is that something that will be fine when it was shut off and be bad the next time it is started?
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Unread 05-25-2011, 05:28 PM   #4
speedbucket
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sounds stuck and needs to be cleaned/replaced
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Unread 05-26-2011, 05:12 PM   #5
Crasher
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1997 ZJ 
 
Join Date: Feb 2008
Location: WI & AZ
Posts: 601
I replaced the IAC valve and started it up. Still idle at 2200 rpm. I unplugged the IAC while running and no change. Then I did what I should have done in the first place. I disconnected the battery for 5 minutes and started it. It idles at 800 like it is supposed to. The ECM must have gotten confused when the battery was low when trying to start the engine. I've had a dead battery before, but this has never happened. I guess we need to look at the simple things before throwing parts at it.
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Unread 05-26-2011, 05:21 PM   #6
ZJ5point2GCL
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Join Date: Oct 2009
Location: Calgary
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Quote:
Originally Posted by Crasher View Post
I replaced the IAC valve and started it up. Still idle at 2200 rpm. I unplugged the IAC while running and no change. Then I did what I should have done in the first place. I disconnected the battery for 5 minutes and started it. It idles at 800 like it is supposed to. The ECM must have gotten confused when the battery was low when trying to start the engine. I've had a dead battery before, but this has never happened. I guess we need to look at the simple things before throwing parts at it.
For some reason i was under the impression you had disconnected the battery
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Unread 05-26-2011, 06:36 PM   #7
Crasher
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Quote:
Originally Posted by ZJ5point2GCL View Post
For some reason i was under the impression you had disconnected the battery
It didn't occur to me to try it until the IAC did't change anything. Over the years, the battery has been down low to where it needed a boost to start and never had this problem. Live and learn.
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