the MAF often doesnt throw a code when its dying. your problems sound exactly like what happened to me when mine went. an O2 sensor would throw a code normally. they have error checking built in, where as the MAF does not.

the catalyst melts very fast when unburned fuel is dumped into it. mine melted because i drove with a single cylinder misfire for half a mile to the next exit on the freeway. i knew it melted because the car wouldnt build boost untill like 4300 rpms, it only boosted 10-12psi (normal is 18 ish). the exhaust sounded different too. sure enough when i took it apart there was a 3" melted ball of ceramic rattling around inside.

 

Ok...well I think I have solved the immediate problem. Ghost you were right...I shouldn't think that swapping wouldnt of done anything without doing it. Cyl 2 was the one that never seemed to have a missfire code. so I swapped cyl 2 and 3. and what do you know...cyl 2 missfires. So i bought a new STI coil and replaced the cyl 2 coil and I havent had another one since. I didn't really think about if one cyl missfires it could cause the others to follow. Cleared the codes and the light has not come back on. But I havent scanned it to see if the p0420 code is in there. If that code shows up it should turn the light on correct?

At times it still seems to run a little rougher than normal but it doenst actually missfire. I saw in the sticky about a the stock CTS sensor being faulty and to replace with a green one...but I am going to search more about that and then put it in the correct section. Thanks everyone for offering your opinion and ideas.

 

i dont know if it will help but i have the same codes on my 2.8 and my problem is one missing tooth on the fly wheel the engine speed sen on my car reads the ring gear teeth i dont know bout the 1.8 justg figured i would tell you