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Unread 12-18-2004, 01:42 PM   #1
katarn444
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Can an O2 sensor cause high idle at startup

When I start my xj it idles great, as it warms up the rpms rise until the engine is at operating temp. Once at 210 degrees it adles fine again. I have tested the tps, iac, map, cps. I have also taken the tb off and cleaned it. I also replaced the iac. I have seached here and jeepsunlimited and have not found a solution.

Can a bad Oxygen sensor cause this. I was thinking that the heating element was dead.

I read a couple of threads about O2 sensors and I tried to test it today but my results were completly off. I read that the voltage should jump around between .2v and .7v. Mine jumps around but between 1v and 5v.

So before I waste anymore time can an O2 sensor cause this problem?
Thank you
Katarn

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Unread 12-18-2004, 02:12 PM   #2
400lbguerrilla
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Depending on how many miles you have on your Jeep you should definitely replace the O2 sensor as a matter of routine maintenance.

Usually around 60-80K is the time to replace the sensors.

And from my experience, yes, a bad O2 sensor will cause a high idle.

Do not replace with a Bosch O2 sensor!!! They are faulty out of the box. Just go to the dealership if you need it right away or go to oxygensensors.com if you can wait a week. They are quite a bit less expensive on this website if you get the Walker brand. Walker buys their bulk sensors from Denso and adds the wires and plugs themselves.
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Unread 12-18-2004, 03:26 PM   #3
katarn444
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I heard that NGK makes the OEM O2 sensors, is that true? If so I can get one for $52 at sparkplugs.com so that would probably be the place I would get it.

I also wanted to add that the cherokee is an 89.

Thank you for your help 400lb
katarn

Last edited by katarn444; 12-18-2004 at 03:57 PM..
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Unread 12-19-2004, 05:11 AM   #4
tibim
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The test is simple: Just unplug your O2 sensor (takes 5 seconds) and start her up. The computer will go into default mode with no o2 sensor input and if your high idle goes away you'll know the o2 sensor is sending bad signals when plugged in.

I haven't had a bad O2 sensor cause high idle, for me it was an erratic idle when mine went bad.

But first thing to do is unplug it and see what happens.

-tibim
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Unread 12-19-2004, 10:38 AM   #5
katarn444
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I did tibim's test and it idles the same as before I unplugged the sensor. So now I am screwed because I have no idea what to do.

Katarn
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Unread 12-20-2004, 02:25 AM   #6
palmrose2
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My idle is actually adjustable. Your 89 might be too.

When I first got mine running it would start and go to about 1500 rpm until it got real warm then it would pull back to about 900 rpm. I adjusted the little screw on the stepper (idle ?) motor so that it starts and runs @ ~ 1200 rpm cold and ~ 700 rpm warm.
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Unread 12-20-2004, 02:08 PM   #7
katarn444
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Do you mean the screw where the throttle cable attaches to the throttle body?
I was thinking about doing this but once warm it idles pretty close to 750 rpm, so I do not want it to go too low. Plus the idle while warming up sometimes goes up to 3000 so this minor adjustment will only help alittle bit. Thank you for the suggestion I might give it a good for the hell of it.

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Unread 12-20-2004, 02:33 PM   #8
hormel26c
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This sounds like a problem with the auxiliary air valve not closing shortly after starting. (I'm trying to remember if that year XJ even has one).

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Unread 12-20-2004, 03:48 PM   #9
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There is an Idle Air Controller mounted next to the TPS. I would advise taking that off and cleaning it out real well. The few times I have had high idle after start up, this was the cause.
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Unread 12-20-2004, 04:39 PM   #10
katarn444
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I did disassemble the entire throttle body and clean it, including the iac, but I will try it again. Also are you supposed to lubricate it at all?

hormel26c, I have never heard of an auxiliary air valve, but I think I would have read about it by now, so I would say I do not have one. Thank you for the suggestion though.

I have another thread going about a plug coming out of the wiring harness near the rear fuel injectors that is not connected to anything, if anyone have any thoughts on that it would be great.


http://jeepforum.com/forum/showthread.php?t=124611

Katarn
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Unread 12-20-2004, 09:08 PM   #11
400lbguerrilla
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If you unplugged the sensor and you had the same idle problem as before then your sensor is BAD!

Your engine is getting the same information whether it is plugged in or not which is NOTHING!
Assuming you let it run a few minutes with the sensor unplugged, replace the sensor and enjoy.
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Unread 12-21-2004, 02:37 AM   #12
tibim
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Quote:
Originally Posted by 400lbguerrilla
If you unplugged the sensor and you had the same idle problem as before then your sensor is BAD!

Your engine is getting the same information whether it is plugged in or not which is NOTHING!
Assuming you let it run a few minutes with the sensor unplugged, replace the sensor and enjoy.
What are you talking about? With the O2 sensor unplugged the computer will just stay in default fuel/air mix mode just like when you first start up. The computer does not start using data from the O2 sensor to control the fuel/air mix until the O2 sensor itself is warmed up to the proper temp that's required for it to function in the first place.

I drove my jeep around for 100s of miles with no O2 sensor plugged in when mine stopped working. Sucks down a little more fuel and taxes the cat a bit but other than that it'll run perfectly fine. The check engine light will come on obviously. Supposedley the check engine light is supposed to come on if the O2 sensor is putting out funky readings too, although when mine went bad it never came on(until I unplugged the O2 sensor).

Try taking your O2 sensor out(it'll take you like 2 minutes) and inspect it for anything obvious. My bad O2 sensor had a rattle when I took it out and shook it because of the broken ceramic inside of it(due to water going up the exhaust pipe).

-tibim
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