Lots of good advice so far. I'd like to add a couple of items. Try taking the throttle body off and giving it a good cleaning with some brake cleaner and an old toothbrush. Just three nuts. The throttle ball joint connection has a small clip holding the two halves together. There's a gasket but you may not need to replace it. Also take the air bypass valve out and clean it out good until the valve is loose and flaps around easily. Check all the vacuum lines and clamp any loose connections. Check the aluminum turbo housing for any leaks. Mine was worn through from rubbing on the intake hot air hose.

Going to back Steve up on this one, The 'Y' switch is power antenna up and down but wouldn't count on the motor being any good.

Lamda was the name given to the feedback fuel system known as "Lamda Sond" just a fancy greek name for oxygen senser.

The turbo coming on late might be a leak or broken spring in the wastegate, do NOT however disconnect the wastegate to experiment. If that happens to be the culprit and you run without any boost control you might end up cleaning off the highway of your broken parts into a 5-gallon bucket with room to spare. The power steering belt needs to be tightened or replaced, I suspect the rubber bushings in the mounts have hardened up some giving you this additional slack. If a tighten wont cure replace the belt going one inch shorter.

Setting the valves, check the FAQ as its chock full of proper procedures, you will however need some special tools to get the valve shims out and you might be inclined to visit a wrecking yard to harvest some more valve shims from junkers. A good pocket full of these will be to your advantage. You can make the tool however if you get a needle nose pliers with a very long snout and bend the jaws to go around the camshaft to pick the shims out of place, as for a compressing tool you're on your own but check on Flea-Bay, I looked for you tonight and didn't find any so you might want to find a volvo dealership and bring some vaseline... You can figure it out from here! While you're at it change the timing belt anyway as its cheap insurance.
I recently drove my neighbors intercooled 700 and even in automatic form that thing was quick past 2400 RPM and pulled like stink to 5000, it doesn't boost up like a Cummins ISC but was never meant to be a high boost engine to start with. Remember an ISC doesn't like to fly much past 2100 RPM so its pressure relationship is different to start with not to mention we are a few liters short to begin with.

Again check the FAQ as it will guide you in the right direction. Flame trap is part of the breather system and keeps backfires out of the crankcase, would like to see that on a chevy motor... Volvos have a slightly different language that in some ways is a bit more descriptive than the general terminology used by GM, PCV is flame trap... Turbo gas motor is unknown outside of the GNX except the poncho turbo grand-am or trashcan of the late 70's and a case of beer will get you a long ways provided you stay off the road during consumption.
Hope this helps and a big CONGRATS on your Volvo purchase.

Badge988

1. Boost: check hoses for cracks and holes.
2. Y switch: antenna lowering switch
3. Cleanout: see the 700/900 FAQ under "features" button above
4. Ditto the valves and timing belt.
5. The turbo can whistle. Tighten the belt using the adjuster mechanism on the side of the p/s pump, first making sure the pulley is aligned correctly with the crank pulley (the p/s pump mounting bracket can wear).