If you have already replaced the oxygen sensors, throttle position sensor (TPS), EGR valve, idle air control (IAC) valve, and cleaned the throttle body, and you are still experiencing a very high idle in your 1999 Dodge Ram 1500 truck, there could be a few other possible causes. Here are some additional troubleshooting steps you can take:
Vacuum Leaks: Check for any vacuum leaks in the intake manifold or vacuum hoses. A vacuum leak can disrupt the air-fuel mixture and cause high idle. Inspect the vacuum lines and connections for cracks, loose fittings, or disconnected hoses.
Intake Manifold Gasket: Inspect the intake manifold gasket for any signs of damage or leakage. A faulty gasket can result in a vacuum leak and cause idle issues.
Throttle Cable: Check the throttle cable for any signs of damage or stretching. A worn or improperly adjusted throttle cable can cause the throttle to remain partially open, leading to a high idle.
Coolant Temperature Sensor (CTS): The coolant temperature sensor provides information to the engine control module (ECM) about the engine's temperature. A faulty CTS may send incorrect signals to the ECM, resulting in a high idle. Consider checking and potentially replacing the CTS.
Idle Air Control (IAC) Valve Circuit: Inspect the wiring and electrical connections related to the IAC valve. A damaged or shorted circuit can cause the IAC valve to malfunction and lead to high idle. Ensure all connections are secure and wires are not damaged.
Throttle Body: While you mentioned cleaning the throttle body, it's worth double-checking to ensure it is entirely clean and free from any carbon buildup. Even a small amount of residue can disrupt the proper functioning of the throttle plate, leading to high idle.
If none of these steps resolve the issue, it may be beneficial to consult with a qualified mechanic or bring your truck to a Dodge dealership for further diagnosis. They have the expertise and diagnostic tools to identify the underlying problem accurately.
