Fuel System Issues:
* Vacuum Leaks: A vacuum leak can cause a lean condition, making the engine idle high. Inspect hoses, intake manifold gaskets, PCV valve, and vacuum lines for leaks.
* Dirty Fuel Injectors: Clogged injectors can cause an uneven fuel flow, leading to high idle. Consider cleaning or replacing them.
* Fuel Pressure Regulator: A faulty regulator can cause excessive fuel pressure, resulting in a rich condition and high idle.
* Faulty Fuel Pump: A failing fuel pump can sometimes cause inconsistent fuel pressure, leading to idle issues.
Ignition System Issues:
* Faulty Idle Air Control (IAC) Valve: This valve controls the amount of air entering the engine at idle. A malfunctioning IAC valve can cause high idle speeds.
* Faulty Throttle Position Sensor (TPS): The TPS tells the computer the throttle position. A faulty TPS can send incorrect signals, leading to high idle.
* Faulty Distributor: A worn distributor cap, rotor, or spark plugs can cause misfires, leading to high idle.
* Faulty Ignition Module: The ignition module controls the spark timing. A faulty module can lead to inconsistent spark, affecting idle.
Other Potential Causes:
* Coolant Temperature Sensor: A faulty coolant temperature sensor can give the computer inaccurate readings, affecting the idle speed.
* Engine Control Module (ECM) Issues: A faulty ECM can cause various engine problems, including high idle.
* Intake Manifold Gasket Leaks: Leaks in the intake manifold gasket can allow unmetered air to enter the engine, affecting idle speed.
* Exhaust Manifold Leaks: Leaks in the exhaust manifold can cause a lean condition, resulting in high idle.
* Throttle Cable Adjustment: A misadjusted throttle cable can cause the throttle to stick open, leading to high idle.
Troubleshooting Steps:
1. Inspect for Vacuum Leaks: Use a vacuum gauge or a propane torch (carefully!) to check for leaks in the vacuum lines and intake manifold.
2. Check Fuel Pressure: Measure the fuel pressure with a gauge to see if it's within the manufacturer's specifications.
3. Inspect the Idle Air Control (IAC) Valve: Make sure it's clean and operating properly.
4. Check the Throttle Position Sensor (TPS): Make sure the TPS is adjusted correctly and that the sensor is functioning properly.
5. Check the Coolant Temperature Sensor: Make sure the sensor is reading the correct temperature.
6. Scan for Diagnostic Trouble Codes (DTCs): Use an OBD2 scanner to see if there are any codes stored in the ECM.
Note: It's important to note that this is a general guide and specific solutions may vary depending on the year, model, and condition of your van. If you are unable to diagnose the problem yourself, it is best to consult a qualified mechanic for further assistance.
