I've been getting a recurring DTC: P0420: Catalyst System; Bank 1: Efficiency Below Threshold No obvious symptoms but I think the economy is reduced (running rich?) It's on a 1.2 12V 2003 Ibiza I have replaced the pre-cat oxygen sensor but the code keeps coming back. The other things that the Ross-Tech wiki says are to check the catalyst and check the intake and exhaust systems. I'm assuming it means check for leaks. The exhaust system I can check easily but the intake system is a little more complex. Where are the places I should check and how do I check? I know there isn't a gapping hole in the throttle body so I assume it will be more subtle.