* Idle Air Control (IAC) Valve: This valve regulates air flow at idle. A dirty or faulty IAC valve can cause rough idling and hesitation, especially when slowing down. Cleaning it (with appropriate cleaner) is often a simple first step. Replacement is relatively inexpensive.
* Throttle Position Sensor (TPS): This sensor tells the computer the position of the throttle. A faulty TPS can lead to erratic idling and hesitation. It needs to be replaced if faulty.
* Mass Air Flow (MAF) Sensor: This sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor can cause a lean or rich fuel mixture, resulting in hesitation. Cleaning it (carefully, with the right MAF cleaner) can sometimes help, but replacement may be necessary.
* Vacuum Leaks: A leak in any part of the vacuum system can disrupt the engine's air/fuel mixture, causing hesitation and rough idling. These can be tricky to find; often require a visual inspection of all vacuum lines and components.
* Spark Plugs and Wires: Worn spark plugs or damaged spark plug wires can cause misfires, leading to hesitation. These are relatively inexpensive to replace.
* Fuel System Issues: Problems with the fuel filter, fuel pump, or fuel injectors could restrict fuel flow, causing hesitation. This is more involved to diagnose and repair.
* Transmission Issues (Automatic): If it's an automatic transmission, issues within the transmission itself could contribute to hesitation, especially during deceleration. This is generally a more complex and expensive issue to resolve.
* Computer Issues (PCM): While less common, a problem with the Powertrain Control Module (PCM) could cause a variety of issues, including hesitation. This is typically the last thing to check and requires specialized tools for diagnosis.
What you should do:
1. Check engine light: Is the check engine light on? If so, get the diagnostic trouble codes (DTCs) read using an OBD-II scanner. This will give you a much better starting point for diagnosis. Auto parts stores often offer free code reading.
2. Inspect visually: Look for any obvious vacuum leaks, loose connections, or damaged wires.
3. Start with the simple and inexpensive: Clean the IAC valve and MAF sensor. Check and replace spark plugs and wires if they look worn.
4. Professional diagnosis: If the problem persists after attempting the simple fixes and/or you're not comfortable working on your car yourself, take it to a qualified mechanic for diagnosis and repair.
Remember safety first when working on your car. Disconnect the negative battery terminal before working on any electrical components. If you're unsure about any repair, it's best to consult a professional.
