No itâ??s not too expensive and it is similar to a fuel injector cleaning, basically itâ??s a chemical treatment, via the intake manifold. I would guess $100 depending one who does it.
You should check the basics, a cracked plug, coil pack or bad wire will cause a ticking sound and sometimes a genuine Knock at idle.
Was the car always driven on long trips? Or is this something new?
And remember, over octane=carbon=degraded performance.
jeff
