1. Check the throttle body. The throttle body is responsible for controlling the airflow into the engine. If it is dirty or obstructed, it can restrict the engine's ability to breathe and cause it to rev low. To check the throttle body, remove the air intake hose and look inside. If it is dirty, clean it with a throttle body cleaner and a rag.
2. Check the fuel system. A dirty or clogged fuel filter can restrict the flow of fuel to the engine, which can cause it to rev low. To check the fuel filter, locate it under the car and disconnect the hoses. If it is dirty, replace it with a new one.
3. Check the ignition system. A weak spark or faulty spark plug can cause the engine to misfire and rev low. To check the spark plugs, remove them from the engine and inspect them for wear or damage. If they are worn or damaged, replace them with new ones.
4. Check the engine sensors. A faulty engine sensor can send the wrong signals to the engine computer, which can cause it to rev low. To check the engine sensors, disconnect them one by one and see if the engine's RPM changes. If it does, replace the faulty sensor.
If you have checked all of these things and the engine is still only revving to 3000 RPM while stationary, you may need to take it to a qualified mechanic for further diagnosis.
