Chapter 25 Computer System Service 425
Computer System Sensor and Actuator Diagnosis
Condition Possible Causes Correction
Hard starting. 1. Faulty coolant temperature sensor.
2. Defective intake air temperature sensor.
3. Maladjusted or defective throttle position sensor.
4. Faulty crankshaft position sensor.
5. Faulty manifold absolute pressure sensor.
6. Bad mass airfl ow sensor.
7. Faulty idle speed motor.
8. Bad fuel injectors.
Test components and related
circuitry. Service or replace as
necessary.
Engine stalling. 1. Faulty coolant temperature sensor.
2. Defective intake air temperature sensor.
3. Maladjusted or defective throttle position sensor.
4. Faulty crankshaft position sensor.
5. Faulty manifold absolute pressure sensor.
6. Bad mass airfl ow sensor.
7. Faulty idle speed motor.
8. Bad fuel injectors.
Test components and related
circuitry. Service or replace as
necessary.
Rough idle or surging. 1. Faulty coolant temperature sensor.
2. Defective intake air temperature sensor.
3. Maladjusted or defective throttle position sensor.
4. Faulty crankshaft position sensor.
5. Faulty manifold absolute pressure sensor.
6. Bad mass airfl ow sensor.
7. Faulty idle speed motor.
8. Bad fuel injectors.
Test components and related
circuitry. Service or replace as
necessary.
Erratic idle speeds. 1. Maladjusted or defective throttle position sensor.
2. Faulty crankshaft position sensor.
3. Bad idle speed motor.
Test components and related
circuitry. Service or replace as
necessary.
Cold engine warm-up problems. 1. Faulty coolant temperature sensor.
2. Faulty intake air temperature sensor.
3. Faulty manifold absolute pressure sensor.
4. Bad mass airfl ow sensor.
5. Bad idle speed motor.
Test components and related
circuitry. Service or replace as
necessary.
Engine hesitation. 1. Faulty coolant temperature sensor.
2. Faulty air temperature sensor.
3. Maladjusted or defective throttle position sensor.
4. Faulty EGR position sensor.
5. Defective or contaminated oxygen sensor.
6. Maladjusted or faulty crankshaft position sensor.
7. Faulty manifold absolute pressure sensor.
8. Bad mass airfl ow sensor.
9. Bad fuel injectors.
Test components and related
circuitry. Service or replace as
necessary.
Continued