* Mass Airflow Sensor (MAF) Sensor: This sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor can provide inaccurate readings, leading to a lean fuel mixture (not enough fuel for the air) and causing hesitation, especially under certain load conditions like cruising at 45 mph.
* Throttle Position Sensor (TPS): This sensor tells the engine control module (ECM) the position of the throttle. A faulty TPS can cause erratic fuel delivery. Similar to the MAF sensor, this can result in hesitation.
* Fuel Filter: A clogged fuel filter restricts fuel flow. At higher speeds (above 55 mph), the engine may demand more fuel, and the slightly reduced flow from the filter may be less noticeable. At lower speeds, the reduced flow is more impactful, causing hesitation.
* Spark Plugs and Wires: Worn-out spark plugs or damaged spark plug wires can cause misfires, resulting in hesitation and loss of power. While this could happen at any speed, the issue manifesting only at a certain speed might be related to engine load at that specific speed.
* Fuel Pump: A weak fuel pump might struggle to deliver sufficient fuel at higher demands, leading to hesitation, particularly at a certain load. This is less likely if the problem doesn't persist at higher speeds.
* Crankshaft Position Sensor (CKP): A failing CKP sensor can cause misfires and hesitation. The specific speed range could be related to engine timing at that speed.
* Intake Air Leaks: Leaks in the intake system can cause a lean mixture.
Troubleshooting Steps (in order of easiest to hardest):
1. Check the fuel filter: This is a relatively easy and inexpensive first step. If it's visibly dirty or clogged, replace it.
2. Inspect the spark plugs and wires: Check for wear, cracks, or corrosion. Replace if necessary.
3. Clean the Mass Airflow Sensor: Use MAF sensor cleaner (available at auto parts stores) to carefully clean the sensor element. Avoid touching the sensor element itself.
4. Have the TPS checked: This usually requires a scan tool to check its voltage output.
5. Check for vacuum leaks: Inspect all vacuum hoses and connections for cracks or leaks.
Important Note: Before attempting any repairs yourself, consult your owner's manual and consider the safety implications. If you're not comfortable working on your car, take it to a qualified mechanic for diagnosis and repair. They can use diagnostic tools to pinpoint the exact problem more efficiently.
The fact that the hesitation is speed-dependent suggests a problem related to engine load and airflow/fuel delivery at a specific RPM. A mechanic with a scan tool can read the engine's data while the problem occurs to find the most likely cause.
