Chapter 25 Computer System Service 431 Copyright Goodheart-Willcox Co., Inc. 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 airflow 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 airflow 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 airflow 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 airflow 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 airflow sensor. 9. Bad fuel injectors. Test components and related circuitry. Service or replace as necessary. Continued