How to confirm failed O2 sensor?

964Patrick · 07-22-2011, 08:07 AM

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

August West · 07-22-2011, 02:28 PM

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?

ja78911sc · 07-22-2011, 03:38 PM

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

Kuchar · 07-22-2011, 04:50 PM

Maybe there is the simplest and cheapest way: http://www.durametric.com/porsche964faultcodes.aspx

bmohr · 07-25-2011, 11:37 AM

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.

964Patrick · 09-22-2011, 12:01 PM

Finally have the car back with O2 sensor replaced. Engine running is much improved! Idle is very steady now.

Makmov · 09-22-2011, 12:28 PM

Quote:

Originally Posted by 964Patrick

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.

07-22-2011, 08:07 AM	#1
964Patrick User Join Date: Dec 2004 Location: Netherlands Posts: 105	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

07-22-2011, 02:28 PM	#2
August West Addict Rennlist Member Join Date: Dec 2010 Location: Redway, CA Posts: 357	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? __________________ - 1990 964 C4 Silver Metallic - 2005 Toyota Tacoma Double Cab - 2006 BMW R1200GS - 2008 KTM 530-EXCR

07-22-2011, 03:38 PM	#3
ja78911sc Addict Rennlist Member Join Date: Nov 2010 Location: Omaha, NE Posts: 532	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 __________________ 1990 C2: GP White, H&R Greens, Bilstein HD's, G-Pipe, RS Clutch, LWF, Rennline Strut Brace, OE Sport Seats, 22MM RSA/M030 Front Sway Bar, 21MM Rear Sway Bar, Walrod Front Bushings, RS Drop Links, 993C4 Engine Mounts, Cup I wheels, (2) OE Oil Coolers 2012 GMC Sierra (Tow Vehicle) 2009 Chevy Traverse (Kid Taxi) 78 911SC (Sold), 84 VW Scirocco (Sold)

07-25-2011, 11:37 AM	#5
bmohr Addict Rennlist Member Join Date: Oct 2010 Location: Annapolis Maryland Posts: 263	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. __________________ 1990 Franken C2 92 3.6 97 tranny 97 interior Cup II's MAF Bola exhaust Apparently my c2 had a 993 inferiority complex

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07-22-2011, 04:50 PM	#4
Kuchar User Join Date: Dec 2007 Location: Warsaw Poland (Europe) Posts: 197	Maybe there is the simplest and cheapest way: http://www.durametric.com/porsche964faultcodes.aspx

09-22-2011, 12:01 PM	#6
964Patrick User Join Date: Dec 2004 Location: Netherlands Posts: 105	Finally have the car back with O2 sensor replaced. Engine running is much improved! Idle is very steady now.