Just changed the spark plugs in my Audi A3 2.0tfsi Quattro after having a cylinder 1 misfire. The misfire seems to have gone but not the engine is now idling high. Could this be an issue where the ECU learning new parameters with the plugs? I've put NGK plugs in, and it also feels a little down on power.
The most obvious cause of high idle is a vacuum leak.
Recheck all your hoses and connections.
I think your question about ECU parameters is spot on. Your ECU may still think it's running with the fault. Reset the ECU by unhooking the battery for 10 minutes, then reconnect and give it a try. No harm, no foul.