I know there are threads on this, but I feel that a lot of situations can be unique. I have a 2004 w/ 1.8T AWM. It has 72,000 miles, and I just bought it 1 month/2000 miles ago. I've done motor mounts, VCG, cleaned MAF, cleaned Throttle Body and other items myself, so i feel that I am capable of doing some work myself to get rid of this code.
I have noticed lately that my gas mileage has been TERRIBLE. most of my recent short trips (City of Chicago, 5-10 miles each) have been netting me in the range of 10-12 mpg by the time I get back (My wife says that her longer trips including highway have been netting 27-28 mpg though). I don't have a CEL, but I thought that something wasn't right with this. So I took it to Autozone and had them scan using their ODB-II tool. It threw two codes:
P0102 - Mass or volume air flow sensor circuit low input
P0420 - Catalyst system efficieny below threshold bank 1
Now, the P0102 is probably my fault, because I had unplugged the MAF sensor to see if it ran better/worse (saw that in some threads) recently, but plugged it back in. In hindsight, probably should have waited until after getting the codes checked.
The P0420 worries me a bit though, especially in conjunction with the terrible gas mileage lately.
What is the first thing that I should check/change to see if I can fix this problem?
Thanks for everyone's help!