And don't forget :

Change the oil every 5000km or once a year !! I use a 10W/60

Sincerly

Mike

Hum, might be a good idea using the Liqui Moly Injection / the Valve Cleaner (used it in an 2003 Seat AZQ engine, I was exited how clean it got until the main bearings failed [honestly another problem]BTT).
You should check the Injectors too. got problems with an exange engine for my A101 Applause witch didn't fire up at all. I took the Injectors from my oold engine and it worked. the injectors were stuck because of gasoline remains witch haddryed out to som kind of Wax.
As Mike said, you should use kind of 10W60 or IMHO 5W50 Oil. If its Possible to drive the car try the Liqui Moly stuff and kepp the rev about 3000 for maybe 50 kms. Also you should check the Intank gasoline pump. Maybe this ones sticky too and should be change (if you want to tune the engine you can honestly install a bigger one (flow/h, pressure)

So Long

Nviduum

Problem is solved, used a product to clean the engine!

Great :-)

Good luck !!!

Mike