* Vacuum Leaks: A vacuum leak can significantly affect idle and low RPM performance. At higher RPMs, the engine's increased power can often overcome the leak's impact. Check all vacuum lines for cracks, holes, or loose connections. Pay close attention to the lines going to the brake booster, PCV valve, and intake manifold.
* Dirty or Faulty Throttle Body: A dirty throttle body can restrict airflow, causing rough idling. The throttle plate may stick or be uneven. Cleaning the throttle body is usually a relatively simple DIY fix. If cleaning doesn't help, the throttle position sensor (TPS) within the throttle body might be faulty.
* Spark Plugs and Wires: Worn spark plugs or cracked/damaged spark plug wires can cause misfires, especially noticeable at idle and low RPMs when the engine is under less stress. Inspect the plugs and wires for wear and tear. Consider replacing them if they look worn.
* Ignition Coil(s): A failing ignition coil can cause misfires on one or more cylinders. This is again more apparent at lower RPMs. Testing the ignition coils is recommended if the spark plugs and wires are okay.
* Mass Airflow Sensor (MAF) Sensor: A dirty or faulty MAF sensor provides incorrect air/fuel mixture information to the engine's computer. This can lead to rough running, particularly at idle and low RPM. Cleaning the MAF sensor (carefully!) with MAF sensor cleaner is worth a try.
* Crankshaft Position Sensor (CKP): The CKP sensor tells the engine's computer the crankshaft's position. A faulty sensor will disrupt timing and lead to rough running, more noticeable at lower RPMs.
* Fuel Injectors: Clogged or malfunctioning fuel injectors can lead to an inconsistent fuel supply. This will affect all RPMs, but the effects may be more prominent at lower RPMs. Cleaning or replacing the injectors is a more involved process.
* PCV Valve: A clogged PCV (Positive Crankcase Ventilation) valve can cause a build-up of pressure in the crankcase, impacting the engine's breathing and leading to rough idling.
Troubleshooting Steps:
1. Start with the simple stuff: Check vacuum lines and clean the throttle body. These are often the culprits and the easiest to address.
2. Inspect the spark plugs and wires: Look for wear, cracks, or damage.
3. Check engine codes: Use an OBD-II scanner to read any diagnostic trouble codes (DTCs) stored in your car's computer. These codes can provide valuable clues.
4. If codes point to sensors (MAF, CKP, etc.): Consider replacing the implicated sensor.
5. If the problem persists: Seek professional help from a mechanic. They have the tools and expertise to diagnose more complex issues.
Remember safety first! Work on your car in a well-ventilated area and disconnect the negative battery terminal before starting any work. If you're not comfortable working on your car yourself, take it to a qualified mechanic.
