Warning! Uneven and unstable idle speed does not always indicate a stepper motor failure. It is necessary to check the reliability of the contact between the plunger and the set screw beforehand.
Stepper motor, suspension plate and plunger
1 - stepper motor, 2 - suspension plate, 3 - plunger
Initial adjustment of the throttle lever screw
1 – stepper motor plunger, 2 – adjusting screw head, 3 – cap, 4 – throttle lever
Checking the correct adjustment of the stepper motor
1 – lock nut, 2 – adjusting screw, 3 – feeler blade, 4 – plunger
Stepper Motor Plunger Positions
1. Remove the negative cable from the battery.
2. Remove the air filter.
3. Disconnect the multi-pin connector from the stepper motor.
4. Remove the four screws that secure the stepper motor mount to the carburetor.
5. Remove the engine together with the suspension.
6. Install the stepper motor, tighten the four screws and connect the connector.
7. Perform an initial adjustment of the throttle lever screw so that the screw head is 7.5 mm from the lever.
8. Connect the air cleaner vacuum hose. Place the air cleaner aside so that you have access to the carburetor and stepper motor.
9. Connect the tachometer according to the instructions.
10. Connect the battery.
11. Start the engine and check and, if necessary, adjust the mixture quality.
12. Disconnect all electrical consumers. If the idle speed control wire is grounded, temporarily isolate it. Check that the automatic transmission gear selector lever is in position N or P.
13. Increase the engine speed to 2500 rpm and return to idle speed, then repeat the cycle. Insert a 1.0 mm thick feeler blade between the stepper motor plunger and the set screw, and the engine speed should be within 875±25 rpm.
14. To make adjustments, remove the protective cap, loosen the lock nut and turn the adjusting screw to set the required idle speed.
15. Remove the chip blade, stop and restart the engine, observing the movement of the stepper motor plunger. After stopping the engine, the plunger should move into the anti-knock zone (retract into the stepper motor), and after a few seconds move to the throttle lever.
16. Disconnect the tachometer and replace the air filter.
17. Recheck the quality of the mixture.
18. Reconnect the idle speed control wire.