Car shaking at idle or a rough idle can stem from simple maintenance (vacuum leaks, dirty throttle, weak battery/alternator affecting sensors) or deeper issues (misfires, mounts, fuel delivery).

Scan for misfire-related codes and watch live data: RPM stability, calculated load, fuel trim, and cylinder-specific counters if available. A flashing MIL usually means catalyst-damaging misfire—reduce load and diagnose soon.

Ignition coils and plugs are frequent culprits on many engines; carboned intake valves and EGR issues appear on direct-injection platforms. Use freeze frame from when the code set to see engine temp and load context.

An OBD2 app with AI explanations can narrow hypotheses, but always confirm with tests (compression/leakdown, smoke test for leaks) before large spend.