Before you do that, however, check to see if the timing belt slipped one notch. That can cause precisely your kind of trouble. Sluggish; no power, runs crappy.

Once you verified that the timing belt is dead-on, then check the ignition timing. See if the timing MARK on the crank pulley is actually where it is supposed to be (verified by cam timing mark with CORRECT timing belt alignment). They spin out sometimes and render the timing mark on the crank pulley useless.

If these things haven't been checked, start here. Then move on to the knock sensor. Checking this stuff doesn't cost money. If a shop does it, you might as well just get a new timing belt installed.

It could be the knock sensor causing problems. At this point, you might as well just replace the thing. You've replaced every other sensor.

Last possible thing: The ignition module (looks like a computer box) on the right hand strut tower. Says VOLVO in big letters... they can fry in a variety of ways. Make sure the vacuum hose is attached to it (Although they run OK with it detached, really). The EFI module inside the car rarely goes bad on these models. When they do, it usually just does not run at all.

As you can tell, still some details to be sorted out, but there aren't that many angles left to play.