I like to change the pid on maf sensor to grams per sec its a little easier for me to look at. plus at idle around 800rpm on most vehicles it will equal the size of the engine ex. that you have is a 2.4liter it will be 2.4 grams per sec idling if its reading right. a easy way to check to see if cat is plugged is by unhooking egr back pressure valve and hooking a pressure gauge snap throttle should have no pressure.
The only reliable way other than using a multimeter in a complicated fashion is to view the live data on a scanner and check the inputs and outputs. Some scanners will even let you graph the data over time and you can see inconsistencies if it is intermittent.
