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Old 12-15-2010, 07:32 PM   #1
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High idle and Trouble Codes

2002 Wrangler, 4.0. It's been idling high at cold startup, about 2000 RPMs and then gradually drops down to normal idle speed as it warms up. We took it to our mechanic and he diagnosed as a faulty coolant sensor, which he replaced. It did not solve the problem and the jeep still idles high at startup.

Today the CEL came on, codes P0135 & P0155 (O2 Sensor Heater Circuit (Bank 1 Sensor 1) & O2 Sensor Heater Circuit (Bank 2 Sensor 1)). I'm sure the codes are related to the idle issue, but not sure how. Is there a bad O2 sensor, or something else? Any ideas welcome.

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Old 12-15-2010, 07:37 PM   #2
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Has there been any work on the engine where the intake manifold has been removed that could cause a vacuum leak? Or any other work involving anything that could have affected anything to do with vacuum lines? A vacuum leak is a common cause of high engine rpms.

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Old 12-15-2010, 07:44 PM   #3
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both upstreams at the same time sounds like something other than the o2 sensors, but the heater circuit is usually the sensor itself failed. sucks if it's both of them...autopart can get you cheap sensors, they're not great, but your wallet will thank you.
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Old 12-15-2010, 07:46 PM   #4
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No work on the intake manifold that I'm aware of however the jeep is getting a little old and I know that the rubber vacuum lines could be suspect. There was a broken vacuum line for the fan selector a while back that I fixed.

What's the best way to check for vac line leaks? I read that you can spray the vac lines with throttle body cleaner and listen for a change in idle speed, which I tried briefly, but didn't notice anything.

I guess one question would be is the high idle causing the O2 codes, or vice versa?

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Old 01-13-2012, 12:47 PM   #5
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My 2002 is doing the same thing. Here's my scenario: Went off-roading and lots of mud so the next day I washed the Jeep and hosed off the engine. Now I get that high idle at startup but its not consistently every startup.....wierd. I visually scanned overthe vacuum hoses and connections but see nothing wierd. My climate control works fine. So I'm hoping it's just a vacuum leak that I cannot see or on a key piece of hardware.
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