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Old 07-22-2011, 09:07 AM   #1
964Patrick
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Question How to confirm failed O2 sensor?

Hello,

My car has occasional rough (high) idle, and overall response is not what I expect it to be. I suspect a failed O2 sensor. Is there a cheap way to confirm this is the culprit? Perhaps by unplugging the O2 sensor and take it for a drive? Would it be harmful for the engine?

Thanks,

Patrick
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Old 07-22-2011, 03:28 PM   #2
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It's a bit of a reach and helps if you remove the blower duct (to get second hand in there) but the connector is mounted with a clip up against the forward left corner of the engine bay compartment (driver's side in LHD cars). It's a simple connector with a rubber boot but it really requires two hands to disconnect and reconnect. Be very careful as the plastic clip that secures the connector wiring is prone to breaking ($2.49 part).

I've found that getting rid of those silly crimp clamps on the ISV valve and replacing them with real hose clamps helped with my idle...I think I was getting some air leakage past the crimp clamps and made my idle hunt. I had to sister two narrow band clamps with each other because I couldn't find a narrow band clamp that had enough circumference that would fit in the groove on the rubber hoses into which the ISV valve goes. This will make sense if you look at the assembly. Good luck!

When was the last time you had a valve job?
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Old 07-22-2011, 04:38 PM   #3
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If you can get your hands on a diagnostic tool (ie, Bosch Hammer), you can check codes.

The sensor is not very expensive (in Porsche dollars), it is easy to replace, and failure is very common--I thought I read that they last around 40K miles on average. Based on this, I would change it.

My idle was hunting and I cleaned the ISV. Did nothing. Replaced the O2 sensor and fixed the problem.

There is a great write-up in the DIY section in refrence to replacing the sensor.

Jim
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Old 07-22-2011, 05:50 PM   #4
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Maybe there is the simplest and cheapest way: http://www.durametric.com/porsche964faultcodes.aspx
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Old 07-25-2011, 12:37 PM   #5
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Replaced my O2 sensor this weekend. Got a good deal i guess. They used to run 120 bucks or more for the direct replacement, but I got mine for 92 bucks. Anyway, of course the sucker was rust welded on. Def have a noticable improvement in the running of the engine. Smoother.
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Old 09-22-2011, 01:01 PM   #6
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Finally have the car back with O2 sensor replaced. Engine running is much improved! Idle is very steady now.
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Old 09-22-2011, 01:28 PM   #7
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Quote:
Originally Posted by 964Patrick View Post
Hello,

My car has occasional rough (high) idle, and overall response is not what I expect it to be. I suspect a failed O2 sensor. Is there a cheap way to confirm this is the culprit? Perhaps by unplugging the O2 sensor and take it for a drive? Would it be harmful for the engine?

Thanks,

Patrick
It should throw a check engine light. Disconnecting the O2 will open loop the circut and cause the mixture to go full rich, which it will like and run out better expecially above 4k rpm. Stock it's very lean for fuel economy and moreover, emmisions.

It really wont hurt the engine, but it could damage the cat over extended periods of time.

There are certianly other things that could cause your symptoms.
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Old 09-22-2011, 01:28 PM
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