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Discussion Starter #1
I have a 2007 SE with the DOHC engine with California emissions that won't idle if the air temp is below about 30 degrees. I live in the frigid north.

It either idles very high (like 2500-3000 RPM) or will not idle at all. After everything warms up and I shut it off and restart it, idle is usually normal or maybe just a little fast. If the air temp is above 30 degrees it usually runs normal.

I have replaced just about everything associated with the idle system: IAC, IMRC, all the associated solenoids, vacuum hoses, even a whole new intake manifold as it originally seemed like a vacuum leak problem. About the only thing not replaced yet are the O2 sensors but I don't get a code from either of those to indicate a problem. I have taken it to a shop I trust and after spending $1000 with them throwing parts at it and trying to tweak the idle via the EDM they told me I had a bad EDM. I purchased a rebuilt EDM and swapped that out. No change.

That's a long description of my issue, but I am really at a lose for where else to look. Any real ideas?

I would appreciate any helpful input.
 

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The high idle rpm says vacuum leak and cold dying says again when the fuel map at idle runs out of fuel. Read the upper O2 sensor and if it stays mostly below .5 volt at idle you are there.
 

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2006 ZX3 2.0, 2006 ZX5 2.0, 2004 ZX3 SVT
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As AMC stated, you have a vacuum leak. Check your pcv valve and hose. Underneath the intake on the driver's side US.
 

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Discussion Starter #6
The high idle rpm says vacuum leak and cold dying says again when the fuel map at idle runs out of fuel. Read the upper O2 sensor and if it stays mostly below .5 volt at idle you are there.
Please interpret the "mostly below .5 volt you are there" part. I don't follow what you are saying.
 

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Normal upper O2 action has the voltage flipping from .9 volt to .1 and equally crossing through .5 as it does. .9 is rich and .1 is lean. When the voltage flipping back and forth lowers to be say .1-.6 you are hanging lean, when you get the 'not switching ' code for O2 then it will be hung around .1-.2 or so, it will never go past .5, the midpoint. Crossing .5 back and forth is the 'switching' any O2 sensor must do to be able to correct A/F ratio both ways.

Fuel trims are another indicator, if the short term one is + and over 10 it is showing the PCM is adding too much fuel trying to make up for a vacuum leak which is too lean.
 

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Discussion Starter #9
Normal upper O2 action has the voltage flipping from .9 volt to .1 and equally crossing through .5 as it does. .9 is rich and .1 is lean. When the voltage flipping back and forth lowers to be say .1-.6 you are hanging lean, when you get the 'not switching ' code for O2 then it will be hung around .1-.2 or so, it will never go past .5, the midpoint. Crossing .5 back and forth is the 'switching' any O2 sensor must do to be able to correct A/F ratio both ways.

Fuel trims are another indicator, if the short term one is + and over 10 it is showing the PCM is adding too much fuel trying to make up for a vacuum leak which is too lean.
Thank you for the information on the O2 numbers. That will give me something to watch that I can understand now next time I hook up my scanner and run it. I agree with you and others that it seems like a vacuum leak. I jusy can't find where that leak might be. As I said, I have replaced pretty much everything that could the cause and still not running right.
 
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