A flickering check engine light with a rough idle on a W177 A-Class usually points to ignition coils, injectors, or a vacuum/PCV issue. Here’s where to start your diagnosis and when it’s safest to stop driving.
First, Understand What a Flickering Light Means
A rough idle paired with a check engine light that flickers in and out is a warning worth listening to. A steady light usually means a constant fault; a flickering one often points to something intermittent — a misfire that comes and goes, a sensor drifting in and out of range, or even a low battery voltage making the electronics behave erratically. One important distinction: if the light is flashing rather than flickering, the engine computer is detecting a severe misfire that can overload the catalytic converter with raw fuel. In that case, ease off the throttle and get the car checked promptly. A flicker at idle, though, is most often fuel, ignition, or air related — very diagnosable.
Read the full breakdown in the Knowledge Base
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