* Ignition System:
* Ignition Coil(s): A failing coil can struggle to provide sufficient spark at higher RPMs, leading to misfires and stalling. This is a common issue with age and heat.
* Ignition Wires/Distributor Cap & Rotor (if applicable): Worn or damaged ignition wires can cause poor spark delivery. Similarly, a cracked distributor cap or worn rotor (if your Millenia has a distributor) can interrupt the spark at higher RPM.
* Crankshaft Position Sensor (CKP): This sensor tells the ECU the engine's rotational speed. A faulty CKP sensor can cause erratic engine behavior, especially under load (like at higher RPMs).
* Cam Position Sensor (CMP): Similar to the CKP sensor, a malfunctioning CMP sensor can disrupt the ignition timing.
* Fuel System:
* Fuel Pump: A weak fuel pump might not be able to supply enough fuel at higher RPMs when the engine demands more. It could be failing or the fuel filter might be clogged.
* Fuel Filter: A clogged fuel filter restricts fuel flow, causing problems at higher engine speeds when fuel demand increases.
* Fuel Injectors: Clogged or malfunctioning fuel injectors could fail to deliver the necessary fuel at higher RPMs. This can manifest as a rough running engine and stalling.
* Fuel Pressure Regulator: A faulty regulator could cause inconsistent fuel pressure, leading to stalling.
* Other Potential Causes:
* Mass Airflow Sensor (MAF): A dirty or faulty MAF sensor provides inaccurate air flow readings to the ECU, leading to incorrect fuel delivery and potential stalling.
* Throttle Position Sensor (TPS): An inaccurate TPS reading can also cause the ECU to miscalculate fuel and ignition timing.
* Vacuum Leaks: Leaks in the intake manifold or vacuum lines can disrupt the engine's air/fuel mixture and cause problems, particularly at higher RPMs.
* Engine overheating: While less likely to directly cause stalling *only* at 3-4k RPM, an overheating engine can cause a variety of problems including misfires and stalling.
Troubleshooting Steps:
1. Check for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to read any stored trouble codes. This is the first and most important step. The codes will give you a good starting point.
2. Inspect visually: Check the ignition wires, distributor cap and rotor (if applicable), and look for any obvious signs of damage or wear.
3. Listen for unusual noises: Pay attention to any unusual sounds coming from the engine, such as clicking, rattling, or whining.
4. Check fuel pressure: This requires a fuel pressure gauge and some mechanical aptitude. Low fuel pressure indicates a problem with the fuel pump, filter, or regulator.
5. Test the components: Testing the MAF sensor, TPS, CKP sensor, and CMP sensor usually requires a multimeter and knowledge of the specific test procedures.
Important Note: Diagnosing this issue correctly requires a systematic approach. If you are not comfortable working on your car's engine, it's best to take it to a qualified mechanic for diagnosis and repair. Ignoring the problem could lead to more serious engine damage.
