To test the coilpacks you have to gap the spark plugs to 0.6 instead of 0.7. If this improves the coughing/spluttering then its a pretty good bet the coilpacks are on their way out. To test the spark plugs; car in 4th gear, 2000rpm, then foot flat on the floor. If you've got dodgy plugs it will start coughing straight away, also will check your clutch at the same time. Olly.