A rough idle that shakes the steering wheel or seat is almost always a misfire, a vacuum leak, or a clogged fuel injector. Pull codes first - the fix is usually a single cylinder.
A weak cylinder shows up worst at idle when each pulse matters most. Codes P0300-P0308 identify the cylinder.
A cracked hose or bad PCV creates lean idle and rough shake. Listen for hissing or use a smoke test.
Carbon buildup disrupts idle airflow stability. Cleaning resolves it 90% of the time.
A clogged injector starves one cylinder of fuel at low RPM. Often produces a single-cylinder misfire code.
A broken or torn engine mount lets normal engine vibration transmit straight into the cabin. The engine is not actually running rough.
The CEL is flashing, the engine stalls at idle, or you smell raw fuel. Flashing CEL means active misfire damaging the catalytic converter within hundreds of miles.
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Misfires and vacuum leaks have biggest effect at low RPM where each combustion event matters most. They get masked at higher RPM.
Yes - worn plugs cause misfires that show up worst at idle. Often the cheapest fix at $40-$150 in parts.
Spray carb cleaner around intake gaskets and vacuum hoses at idle. If RPM rises momentarily, you found it.
Usually yes if the cause is plugs, coils, or fuel filter. Not if its a sensor, injector, or mount issue.
Continuous misfires destroy catalytic converters and wash oil off cylinder walls. Fix within a few weeks.