I have done a high pressure boiling soapy water wash before. On my 1.7, 1.6 NA, 1.6 TD, 1.8 Digi, and 1.9 M-TDI.. I have never had the problems you describe. When you say "slow to start" what exactly do you mean? it takes more cranks to fire off? or the starter is physically turning the engine over slower?
There are a few things to address, did you get any water in the intake?? This is important, as if you did.. bad things have happened. Now you would have had to get quite a bit, but a few drops in to any one cylinder could be catastrophic. As you may well know water is not compressible, therefore getting some in a cylinder that already gets up to 400-500psi.. would mean havoc somewhere, and its usually the weakest link. The connecting rods.
NOW, if you are sure you didn't get any water in the intake then it is a whole other ball-game. If it were just a garden hose with or without a nozzle.. there isn't enough pressure there to knock anything loose really.. plus, you've said it yourself a simple beast, so you know there isn't much to knock loose to begin with.
Check the pumps power wire, check your fuel lines, get rid of the air bubbles. Power to the pump so it can pass fuel, and air is all that is needed.