MK4 2.0L petrol engine APK oxy sensor

[Lyle]

Hi team, how many oxygen sensors should the APK engine have? I only have 1... it’s the one under the bonnet in the back of the exhaust near the firewall. There is NO sensor post cat, and it doesn’t feel like there’s a threaded hole for one in my cat either?! I had it replaced in March as the guy I bought it off knocked it through. I’m asking because I suspect a faulty O2 sensor: I’m having a somewhat rough idle - feels like the car goes into limp mode intermittently when it warms up, and is running super rich. Having the codes read Friday, but any info on what is normal O2 set up would be helpful. Cheers!