Rough running

Using a legacy scanner like INPA, ISTA+, DeepOBD, ProTool etc. You can access the engine rough running menu. It allows you to check whether engine is balanced at idle or not Values must be between -200 and +200. The closer to zero, the better. Depending on the version of the diagnosis tool, the Limits might be -2.00 and +2.00.

The same tools can be used to display the spark ignition latency (spark duration) per cylinder, in milliseconds.

Idle Low load/Low RPM Overrun/Deceleration High load/Low RPM
2.1 ~ 2.3 2.2 ~ 2.5 2.5 ~ 2.8 1.0 ~ +
Common causes

Eccentric shaft sensor agin (Oil contamination inside the sensor circuit board) Vanos Solenoids partially-clogged (excessive backpressure at idle) Cylinder head non-return filter valves partially-clogged External (post-MAF) vacuum leak Faulty MAF Internal vacuum leak (Worn piston rings in one/multiple cylinders) or bent/burned/coked cylinder head valve Torn CCV diaphragm or cracked vacuum hose Partially-clogged catalytic converters Partially collapsed HVA lifter Demagnetized camshaft sensors Aging upstream oxygen sensors Bad quality gasoline (Water, low or inconsistent Octane, dirt) Agin spark plugs and/or ignition coils Timing chain slack
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