This might help,

I had similar mileage then you (around 250-300Kms per tank). I did the full tune up (with Autolite plugs), cleaned the intake manifold (completly took it off and cleaned it with carb cleaner and a toothbrush). This got me around 350-380 kms per tank.

The one thing that really made a huge jump was to have my injectors cleaned using the Snap On Motorvac. From what I've read when I had a Volvo, this is the best system to clean the fuel system. (You can take a look at www.brickboard.com in the Volvo 700/900 FAQ for complete information or I can copy paste it here). By doing this, I now do about 450-480 Kms per tank

I need to change my IAC and the bank 1 O2 sensor since I'm also getting the intermitent CELs.

I hope it helps.

Eric

PT Cruiser Limited 2002 MTX of course! Mystique 1998 V6 MTX Sold.