New to me 02' 986 S

[shadrach74]

I recently picked up a 2002 986 S with 52K that has some issues. And I have some questions for those that know more than me.

The car threw a CEL in the first 50 miles (leading me to believe that the last owner turned it off prior to sale) I am getting a P0430 (Catalyst System Efficiency Below Threshold (Bank 2) and the car does not seem to run in keeping with what I would expect from a 250hp machine that weighs just 2900lbs. My gf's Mini C S will run with it for the most part. The main difference between the 2 is that I average about 25 to 27MPG when driving hers and I about 14.9 with 986 through my first 3 tanks of gas (seems excessive even considering my spirited driving style). It does not appear to be running extremely rich, as I'm not getting any soot from the exhaust. Howevreeee

I have purchased a set of used (40K) cats (with O2 sensors) to at least try and figure out if it is an O2 issue or the catalyst. I plan on putting new sensors in when I change the cats.

What oil do you recommend for this engine? I plan on replacing the plugs as well.

RMS is leaking. How big of a deal (yes, I'm familiar with the IMS issues on these cars) is it to run it until it's time for a clutch?

What would you check right out of the gate to ensure that you are meeting stock levels of performance? It handles beautifully, but the engine feels like not living up to it's potential. I doubt that I'll keep this car long term. It will likely be sold in favor of buying a car that has already been performance built.

All input is appreciated!

Cheers!

Ross