Washing the engine
Steam and water cleaning older engines with fuel injection is always a little bit risky. Humidity getting into some parts can make re-starting a challenge. Note that we don't speak of permanent damage, only that you'll have to wait or dry those parts with compressed air. If you do this yourself, there's no problem, but at a garage, when other cars queue up behind you, it can be bothersome.
To be on the safe side, wrap the distributor, coil, airflow sensor, throttle position switch and other related parts into plastic bags and don't direct high pressure water flow directly onto them. I use regular cleaning, grease cutting products on the dirtier spots, loads of kitchen paper towels and a common garden hose with a nice, pistol-shaped nozzle. It's easy to aim with, and it can be operated briefly by pushing its valve button for a second or so. I clean my engine once, maybe twice a year, on a warm, sunny spring or fall day, and never ever had any starting problems. To tell you the truth, I also spare the plastic wrapping and take care of where I aim with the water instead (although a little bit of water won't harm the wiring and the connectors, why should we spray them intentionally?). Granted, it's more tedious than going to a non-specialist garage and letting them attack the engine--but a lot safer.
Note that a thin layer of oil, although it might spoil the shiny look of the metallic parts of the engine, does an excellent job of protecting from corrosion. If you wash it off, your engine bay might start to rust. There are special products like Valvoline Engine Guard which form a transparent, invisible protecting film on the surface. You should consider using them after you have cleaned the engine.