Hi Peter I own a 2001 Golf V5 and had exactly the same symptoms. Bought it cheap cos I thought it was running on 4 cyls sometimes, but was unable to find any cylinder that didnt make a difference. It was due a service so I fitted new vw plugs(even though they were not due for replacement), forte engine flush and injector cleaner. Used good quality oil and then cleaned and reset throttle housing. Also found a split plastic hose on the intake pipe. It ran like a new car after that.