The brief
Mr Jeff Wee had already had the ignition coils and spark plugs replaced on his Touran by another workshop, but the persistent vibration while driving was still there. He came to us for a second opinion, because when the obvious ignition parts are new and the misfire remains, the cause is somewhere else. A misfire isn't only an ignition problem. The fuel injectors spray fuel into each cylinder, and over the years they get dirty or partially blocked, so the spray pattern goes off and that cylinder doesn't burn cleanly, even with a perfect spark. The result is a misfire, a rough idle, stuttering, slow throttle response, and a vibration on the move. Worn or plugged injectors don't clean themselves back to spec, so they get replaced.
The diagnosis
On the lift the Touran got a step-by-step inspection, and the precision scan read misfire fault codes on cylinders 2, 3 and 4, more than one cylinder, pointing at the fuelling rather than the ignition that had already been done. The fuel injectors were worn, which is the misfire and the vibration. The coils and plugs were new and fine. That's a fuel injector replacement, the actual cause, rather than redoing ignition parts that weren't the problem.
The work
The worn fuel injectors were removed, which is extensive dismantling work, and a full set of new genuine VW-spec injectors fitted, the fuel rail and seals checked, the system primed and pressure-tested for leaks. The misfire codes were cleared and the adaptations reset so the engine relearns on clean injectors. A road test confirmed a steady idle, no misfire, no vibration, smooth throttle response, no warning lights, and clean pull through the revs.
The outcome
A steady idle, no misfire, no vibration on the move, smooth throttle response, no warning lights, and the running back to normal. Mr Jeff Wee got the Touran back smooth at last. The coils and plugs being already new told us to look at the fuelling, so replacing the worn injectors fixed the misfire that the first round of parts couldn't, which is the value of a proper second opinion.
