The brief
The Touran had been idling rough, the RPM uneven, with vibrations through the car and the odd stumble at a standstill. He brought it in. A rough idle like that often comes down to the spark plugs. The plugs light the air-fuel mixture in each cylinder, and they wear a little every time they fire. When they're worn, the gap opens up and the spark gets weak, so the combustion goes incomplete in one or more cylinders, which is the uneven RPM, the vibration and the stumble. Worn plugs don't just make the idle rough, they hit fuel economy and can lead to misfires, so it's worth getting them checked rather than living with it.
The diagnosis
The plugs came out and went on the bench. They were worn, the electrodes rounded off and past spec, well into their replacement window, which explained the rough idle. A diagnostic scan confirmed no other underlying fault. So it was a straightforward plug-only job, a fresh set to bring the combustion back to clean.
The work
Four new genuine VW-spec spark plugs went in, gapped as supplied and torqued to the manual's figure so each one seals and conducts heat properly. The coil packs were reseated on top with the harness clips clicked home, and the engine run at idle to confirm it was firing cleanly on all four with no stumble. A road test followed to confirm it idled steady and pulled cleanly through the rev range.
The outcome
Steady idle, even RPM, no vibrations at a standstill, no stumble, and no fault codes. The Touran went home running cleanly. Plugs are a wear item and once they're tired they drag the idle and the running down with them, so a fresh set was the cheap fix that sorted it.