[GATOR*DAWG]

My XUV590i S4 works fine one day and shows the dreaded wrench the next, wait a week and its fine again. It appears to me that when the trouble light (wrench) is on that it is in limp mode as it has very low power. When the wrench is on it idles fine but if I let it idle long the muffler gets so hot it glows orange. I saw one post that was similar that said it might be the O2 sensor, but the intermittent part has me baffled. Please don't tell me to take it to the dealer, that is a huge hassle and expense. This JD has very few hours and miles and should not be having this problem.

 

[MBDiagMan]

Okay, I won’t tell you to take it to the dealer, but you will have to get trouble code if you want to know what trail to take forasolution.

 

[GATOR*DAWG]

The engine is obviously running too rich when the wrench light is on and it appears to be in limp mode thus the orange tail pipe. So with these symptoms and the intermittent thing I am thinking it has to be a sensor that is working sometimes and not at others. Would a O2 sensor work intermittently?

 

[200mph]

Sensor could be fine but the wire connection could be an issue.
Could check voltages when running ok and poorly to see if difference.

added in edit: Voltage into an out of sensor.

 

[GATOR*DAWG]

It could be a wire, I do have a rodent problem, found some seed shells on the manifold near where the wire from the O2 sensor travels. I will check that a little more. Thanks!

 

[Fiveoracing]

My 590 did exactly the same thing. Unplug the sensor and see if it runs better at high rpm but idles bad. If it does the sensor is bad.