The only good method to clean dirty injectors is to run a pressurized can of injector cleaner (like Motorcraft or 3M) directly through the injectors as described in an old service bulletin BUT it requires a special adaptor hose only available through Kent Moore tools (through a Volvo dealer IF they even know where to look for the info?). I have done this proceedure myself (own that adaptor) on many of our customers cars and my own with great results.

As for adjusting your own valves, checking the valve lash is easy yourself (if they're noisy, ticking) but you can't change the clearances without the 2 special tools and a micrometer (not cheap) and a box of selectable valve shims handy unless you don't mind making a trip to your dealer to see what they've got or need to order if not in stock (could be a pain).
Before checking the above two situations further, make sure you havent overlooked more obvious and easier to remedy problems like mentioned in this thread (dirty throttle body, plugs, dist cap, rotor, check ign. wires with an ohm meter(2-4K ohms is normal resistance), vacuum leaks, etc).