AusLegacy

Have to agree with the Seafoam option. Have had a very similar problem on my '91 legacy, and a blast of carby/intake cleaner did the trick ( didn't use Seafoam just a standard Intake cleaner that does not clog Cats.)

240,000 KM (150,000miles )on the clock and getting around 8.5km/l . Have changed my O2 sensor myself (about US$40 for the part). Didn't seem to improve fuel economy though. I recently put some fuel additive in (one thats says that it wont clog the cat.) and power improved dramatically (near the end of the tank) Haven't calculated the mileage yet.

Thanks Josh, i did a quick search and found some great information ( http://auto.howstuffworks.com/framed.htm?parent=question482.htm&url=http://www.autosite.com/garage/subsys/catalyti.asp ) . Testing the vacuum, the pressure at the O2 sensor, the temperature before and after the Cat and knock testing the cat. All probaly worth a try.

She revs well over 5G. I have read that if your exhaust pressure is above 5psi (measured at the manifold with a pressure gauge) then the catalytic converters could be clogged. (I haven't tried it)

Colin, Could you put me onto the the Mechanic that did the carbon clean out, I'm having the same problem.

do a search for this; "The Saga's Final Outcome" Grounded1 had similar symptoms and finally found that catalytic converter to be the problem.