* Fast Idle Cam: This is a common culprit. The fast idle cam is a mechanical device that raises the idle speed when the engine is cold to help it warm up faster. If this cam is sticking or not returning to its normal position after the engine warms up, the idle will remain high.
* Vacuum Leaks: A vacuum leak can cause the engine to take in more air than it should, leading to a higher idle speed. Check all vacuum lines for cracks, looseness, or disconnections. Pay close attention to lines connected to the brake booster, PCV valve, and the intake manifold.
* Throttle Position Sensor (TPS): A faulty TPS can send incorrect signals to the engine computer (if your Ranger has one – some '89 models are carbureted, some fuel-injected), causing an elevated idle.
* Idle Air Control (IAC) Valve (if fuel-injected): The IAC valve regulates air entering the engine at idle. A dirty or malfunctioning IAC valve can cause a high idle.
* Dirty Throttle Body: Buildup of dirt and grime in the throttle body can interfere with the throttle plate's movement and cause a high idle, especially if the fast idle cam is involved.
* Air Filter: While less likely to cause *such* a high idle, a severely clogged air filter restricts airflow, causing the engine to compensate by increasing the idle speed.
* Problem with the Engine Control Module (ECM) or related sensors (if fuel-injected): A faulty ECM or a problem with other sensors (like the coolant temperature sensor) can affect the idle speed.
* Carb Issues (if carbureted): If your Ranger is carbureted, several carb issues can cause high idle, including incorrect adjustment of the idle mixture screws, a vacuum leak in the carb itself, or a sticking throttle linkage.
Troubleshooting Steps:
1. Check the fast idle cam: Manually operate it and make sure it returns smoothly to its resting position once the engine is warm.
2. Inspect all vacuum lines: Look for cracks, loose connections, or any signs of damage.
3. Check the air filter: Replace it if it's dirty.
4. Clean the throttle body: Use a throttle body cleaner and carefully clean the throttle plate and surrounding areas.
5. If fuel-injected, check the IAC valve: Clean it or replace it if necessary. Consult a repair manual for your specific model.
6. If fuel-injected, have a mechanic check the TPS and ECM. This usually requires specialized tools and knowledge.
If you're not comfortable working on your vehicle yourself, take it to a qualified mechanic for diagnosis and repair. They can properly diagnose the problem and avoid further damage. Providing them with the high idle RPM (1100) will be helpful information.
