Unstable idling at Mercedes-Benz S-class (W221), check the value of the SO/C concentration in the exhaust gas at revolutions of about 2,500 rpm.
- If the CO level is normal and the CH is high, then the problem usually consists in the improper clearance of the valves, the malfunction in the ignition system, depressurization of the cylinder block or outlet/exhaust manifold.
- If the CO level is low and CN is high, the crankcase ventilation hose may be the cause.
- If the level and CO and the CON are high, the malfunction may consist of an engine control system, a crankcase, injector or air filter.