Rough idle
Rough idle is an uneven engine speed when the car is stopped and the throttle is closed.
The tachometer hunts, the body shakes, or the engine almost stalls at a light. Misfire codes, a sticky idle valve (P0505), or a lean mixture (P0171) are common companions.
Note whether it happens only when cold or also when warm. That detail, plus the stored code, narrows the next test.
A trouble code marks a condition to test. It does not by itself prove which part to replace.