P0430 code after filling up.. cats have less than 6k miles.. help

[Cavy]

I just bought a 02 996 cabriolet. It had been sitting for awhile due to engine rebuild. Test drove for at least 70 miles no code. Ran fine. Scanned it before buying.. no codes, no pending codes, no deleted codes. 

Driving home the gas tank got to just under 1/4 tank and it started surgining/ bucking. Stopped filled up with 93. Better but still surging. Then the light came on. Stopped and put Techron in and reset light. Drive fine for almost 200 miles.. no light.  Filled up again... light came back on shortly after P0430 

cats and sensors were replaced 2 years ago. Less than 6 k miles since 

I do get some  blue smoke on cold start up. Not a lot. Goes away when warm. Also get squealing noise in cold start. Goes away pretty quick. Sometimes I can hear squealing when warm but very faint 

I hooked my scanner up. Pre o2 sensors bouncing around pretty good and post pretty steady at .7

 

 

Any ideas? Fowler plug from old gas? AOS?  Or could it really be the cats even though pretty new 

Edited September 1, 2019 by Cavy
Addition

[Ahsai]

P0430 (or 0420) takes a while to be tripped (a couple of days of driving with mixed load) because there are a series of tests under different driving conditions need to be run first.

 

Can you check what are the O2 sensor readings at moderate load and constant speed on a flat road? It may be difficult to tell visually since the post O2 will swing as well but should they should swing less than the precat O2 sensors.

 

Squealing could be a failing AOS. You may want to check your crankcase vacuum with a manometer (should he around 5 inches odlf water vacuum).

[Cavy]

It was difficult to really see while driving but at constant speed with consistent gas the post cat  seemed to stay pretty steady unless I let up on the gas. Depending on how much gas I was giving or not it was bouncing all around. 🤷‍♂️