I recently have been having more rough idle on my car and was wondering if it might be the 02 sensors. For a while, in the summer, when the car had been driven for a while, starting it up on first try or 2 the engine would crank but then immediately die, and then if I held the gas down a little while cranking, I could get it working. I cleaned out the throttle body, air filter, and MAF recently, but that didn't change the problem. After changing transmission fluid recently, the car ran really rough immediately after, not wanting to stay cranked unless I constantly pumped the gas, but then after about 5 min of that, the car stabilized and hasn't had that symptom anymore.

I've attached a video of my diagnostic tool while the car is sitting at idle to see if anyone sees anything abnormal with the 02 sensors. I am not familiar with looking at this reading and being able to tell which 02 are the pre-cat and which ones are the post-cat. I'm at 90k miles. Any thoughts?

http://swaffproductions.com/porsche/02.MOV

Swaff

 

when were the plugs changed?

 

Did plugs about 15k miles ago and replaced one coil pack that was split. I am currently not having any CEL though.

Swaff

 

IIRC, O2S12 is bank 1, position 2 (after the converter) while O2S21 is bank 2, position 1 (ahead of the converter).

The #1 sensor (the one ahead of the converter) should have its voltage reading swinging from under 0.1 volts to over 0.7 volts at idle around once a second. However, the tool will not be able to read the voltage level fast enough so you will not see the wave form digitally. To see the wave form you need an analog scope to view the voltage wave form.

The #2 sensor (the one after the converter) should have its voltage reading fairly stable at around/above 0.7 volts. It varies a bit but the magnitude is much less than the #1 sensor.

The O2S12 looks sick based on the short clip you posted. Or the converter is sick. A low reading like that is an excess of oxygen in the exhaust gas and this suggests the converter is not able to hold on (store) oxygen to use for processing the exhaust gases. However, there can be other explanations for what you are seeing. And you are not providing a full picture. It would be nice to see all 4 sensors and the short term fuel trims and the MAF reading.

Often just one sensor is bad -- though of course a common failure can make all on one back or all 4 look bad -- so if you can view all 4 concurrently you can often spot the bad one as it does not produce the same readings as its counterpart on the other bank.

Are there any active DTCs? What about any pending DTCs?

 

Hey Macster, no DTCs or pending DTCs...

Swaff