* Automatic Choke (Thermo-Wax Actuator): This is the primary component controlling cold idle speed. As the engine warms, the wax in the choke element melts, gradually reducing the airflow restriction and lowering the idle speed. You can't directly adjust this. A malfunctioning choke (stuck open or closed) is the most likely culprit for an excessively high or low cold idle. If it's sticking, it might need replacement or cleaning (with caution, as they're delicate).
* Air Flow Meter (AFM): This measures the amount of air entering the engine and plays a role in fuel delivery calculations. A malfunctioning AFM can lead to improper cold idle. It's crucial the AFM is clean and working properly. Cleaning it with MAF cleaner is sometimes effective, but replacement might be necessary.
* Throttle Position Sensor (TPS): While not directly impacting cold idle as much as the choke and AFM, a faulty TPS can disrupt the overall engine management, indirectly affecting the cold idle speed.
* Computer (ECU): The ECU receives input from the AFM, TPS, and other sensors, influencing the fuel mixture and idle speed. Issues with the ECU are less likely to be the sole cause of a high cold idle, but a malfunctioning ECU can indeed affect it.
Therefore, directly lowering the cold idle speed on a 1991 22R is not recommended without addressing potential underlying issues. Instead, focus on troubleshooting these components:
1. Check the choke: Observe its operation as the engine warms. Does it close fully when cold and gradually open? If not, suspect a faulty choke.
2. Clean the AFM: Use a specialized MAF cleaner (NOT carb cleaner). Carefully clean the sensor element according to the instructions.
3. Inspect the TPS: Make sure it moves smoothly and reports the correct voltage to the ECU (consult a repair manual for specifics). Testing the TPS is best done with a multimeter.
4. Check for vacuum leaks: Vacuum leaks can significantly affect idle speed. Inspect all vacuum lines for cracks or loose connections.
5. Diagnose the ECU: This is more difficult. An OBDI scanner (if one's available for this system) or a professional mechanic would be needed.
In short: Don't try to adjust anything related to the idle speed directly. Fix the underlying problem causing the high cold idle – a faulty component is much more likely than a simple adjustment screw. A repair manual specific to your 1991 Toyota 22R will be your best friend during this process.
