VW CC 2010 2.0L CBFA I installed an O2 sensor spacer on my downstream O2 sensor and it seemed to be working for a day. One day later, after the car had cooled down it would rough idle and stall when i started it for the first time in the morning. Removing the spacer fixed this.
I have read everywhere that downstream O2 sensors aren't used by the ECU at all and are only used for emissions. How is this possible?
Here is the spacer i used from amazon. https://www.amazon.com/dp/B00B1U6I54/ref=cm_sw_em_r_mt_dp_U_Cey9CbDH3SGW1
Here is some logging I did for the sensors.
Not shown is short and long term fuel trim which were both steady -1% to 1%