in the states there is a process called MotorVac www.motorvac.com which is used even at some dealerships for over two decades. it is the same basic process.

 

congratulations and welcome aboard. the intermittent problem codes with the coil packs could be a result of playing with the garden hose in the engine bay or worse a pressure washer by a detailing shop. this might have been done by the owner just prior to sale. the water fills the wells where the spark plugs insert and then ruins the electrics. as the car cools, the water is sucked into the coil packs' seals. there is no major issue with a car wash other than it is not good for long term paint condition. these cars were designed and built by the people who invented rain. mine just two days ago traveled for over two hours in that torrential downpour that we had here in NYC, no problems. it is when the bonnet is open and you start spraying the engine covers. water can accumulate under the intake manifold and in the spark plug wells. you can wash the entire engine bay excluding these areas without problems, including the sides of the engine, simply do not use a forceful jet of water.

also, if you change the battery, let the car set depowered for a while to reset everything. however your model year requires more resetting than the older ones after changing the battery. clean the battery's new terminals and the cable clamps before connecting. YOU SHOULD NOT DO this yet if your state performs an OBDII scan to pass as it will clear your data. you can check if you are ready to test with most code scanners.