What could be the reason for the idling vibration in a Nissan Sunny manual transmission? I've replaced the spark plugs, but it hasn't solved the issue.

Start by eliminating one issue at a time. First, clean the throttle body, then check the ignition coils. Ensure the idle motor is functioning properly. Also, consider if the car has high mileage. Check for serious carbon buildup in the intake manifold and whether the air flow meter is working correctly. It's recommended to find a reliable repair shop for an inspection.

Same here, the mechanic said it's hard to fix.

Replace the engine mount. Check the fuel pump. Clean the throttle body.