I have a 99 S80 T6 with about 37K Miles on it. Recently, when I floor the accelerator pedal and during this Wide Open Throttle (WOT) position, the car initially responds beautifully, the initial sensation is that the car is pulling forward very strongly then within 4-5 seconds and above 4000 RPMs seems to back down a bit, then surges up again etc. This fluctuation in power happens every 4-5 seconds as long as the car is in WOT. Although the car is very fast, the solid pinning you to the seat sensation at WOT throughout the power band is fading....now I get that initial kick in the pants followed, like I said, with a type of surging sensation every 4-5 seconds....it just doesn't pull strongly and continuously with the gas pedal floored as it used to when it was newer, if you know what I mean.

I've got a K&N filter installed, Denso Iridium Plugs...everything's working, the air filter is clean, am running Mobil 1 Trisyn in the crankcase and have had the car for a while....I use premium fuel..there's no water in the tank, I used injector cleaner, which didn't help. The car is a gem and still under warranty.

What do you guys think is happening? Is my inline fuel filter clogged or clogging? Is there a fuel filter inside the gas tank too on the intake tube that I may need to change? Are the wastegates on the turbos screwed up or in need of adjustment? Are the turbo pipes leaking boost pressure? Can I tweak anything? Anyway, if this surging has happened to anyone with an S80 what was the solution. Sorry for all the questions, but please...I would really appreciate your input out there. Thanks.