Engine Controls - Trouble Shooting - No Codes: Other Mazda MX-5 NB

HARD TO START (CRANKS NORMALLY)

1. Check fuel pump volume.
2. Check condition of spark plugs.
3. Check coolant temperature sensor resistance.
4. Check air intake system for restriction.
5. Check EGR valve and solenoid for correct operation.
6. Check for cracks and poor connections at mass airflow sensor or throttle body.
7. Check ignition coil resistance.
8. Check by-pass air control valve.
9. Leaking fuel injectors.

NO START (CRANKS NORMALLY)

1. Check fuel pump volume and pressure.
2. Check fuel pump relay.
3. Check condition of spark plugs.
4. Check by-pass air control valve.
5. Ensure crankshaft position sensor has correct resistance value.
6. Check for cracks and poor connections at mass airflow sensor or throttle body.
7. Check ignition coil resistance.

ROUGH OR UNSTABLE IDLE

1. Use stethoscope to verify fuel injector operating noise.
2. Ensure fuel system pressure is correct.
3. Check EGR valve condition and operation.
4. Verify ignition timing is correct.
5. Check PCV valve.
6. Check mass airflow sensor.
7. Check coolant thermosensor for correct resistance.
8. Check by-pass air control valve.
9. Check for cracks and poor connections (vacuum leaks) at airflow meter or throttle body.
10. Check HO2S for fluctuating 0.1-1.0 volt output while increasing and decreasing engine RPM.
11. Verify throttle position sensor adjustment and resistance value.
12. Check purge valve function.
13. Check for poor fuel quality.

HIGH IDLE AFTER WARM-UP

1. Verify correct throttle body dashpot adjustment (if equipped).
2. Check bypass air control valve IAC valve operation.
3. Check air intake system for leaks or restriction.
4. Check throttle cable adjustment.
5. Check coolant temperature sensor resistance.
6. Check airflow meter for cracks. Verify correct airflow meter operation and resistance value.
7. Check ignition timing.

Cold

1. Ensure air filter element is clean.
2. Check fuel filter for restriction.
3. Check EGR valve condition and operation.
4. Check for mass airflow sensor or IAC valve malfunction.
5. Ensure fuel system pressure is correct.
6. Check air intake system for vacuum leaks.
7. Check coolant temperature sensor resistance.
8. Verify correct throttle position sensor adjustment.
9. ECM/PCM malfunction.

Warm

1. Check PCV system for restrictions.
2. Check by-pass air control valve or IAC valve for malfunction.
3. Check connections at mass airflow sensor or throttle body.
4. Check operation of lock-up torque converter.
5. Check coolant temperature sensor resistance.
6. Ensure fuel system pressure is correct.
7. ECM/PCM malfunction.
8. Check throttle bore for dirt and carbon.

ENGINE MISFIRES OR HAS LACK OF POWER

1. Verify air filter is clean.
2. Check fuel filter for restriction.
3. Check closed throttle position switch.
4. Check coil resistance.
5. Check mass airflow sensor for cracks.
6. Check EGR valve and solenoid for correct operation (if equipped).
7. Ensure fuel system pressure is correct.
8. Check purge control valve operation.
9. Check atmospheric pressure sensor.
10. Check ignition system for intermittent operation.
11. Check for restricted catalytic converter.
12. Check Variable Resonance Induction System (VRIS) for correct operation (if equipped).
13. Check Variable Inertia Charge System (VICS) for correct operation (if equipped).
14. Check crankshaft position sensor.
15. Check Lysholm compressor system (Millenia 2.3L) for wear or malfunctioning parts.

ENGINE RUNS ROUGH ON DECELERATION

1. Verify idle speed is correct.
2. Verify correct throttle body dashpot adjustment.
3. Check coolant thermosensor and throttle position sensor.
4. Check by-pass air control valve or IAC valve for malfunction.
5. Check fuel pressure regulator.
6. Check HO2S operation.
7. Check throttle position sensor and closed throttle switch.
8. Check airflow sensor operation.

BACKFIRE IN EXHAUST SYSTEM

1. Verify base timing is correct and advance system is functional.
2. Check throttle body dashpot adjustment (if equipped).
3. Check coolant temperature sensor and throttle position sensor.
4. Check air valve, ISC switch and idle switch operation.
5. Check intake air system and throttle body electrical connections for vacuum leaks.
6. Ensure fuel system pressure is correct.
7. Verify no leaks exist in exhaust system.

POOR FUEL MILEAGE

1. Check injectors for leakage.
2. Verify correct throttle body dashpot adjustment.
3. Ensure correct throttle position sensor adjustment and resistance value.
4. Check intake air and coolant temperature sensors.
5. Ensure fuel system pressure is correct.
6. Ensure exhaust system is unrestricted.

EXCESSIVE OIL CONSUMPTION

1. Check for restricted PCV system.
2. Check for worn engine parts.

Intermittent Simulation

To reproduce conditions creating an intermittent fault, use the following methods

1. Lightly vibrate component.
2. Heat component.
3. Wiggle or bend wiring harness.
4. Spray component with water.
5. Remove/apply vacuum source.

Monitor circuit/component voltage or resistance while simulating intermittent. If engine is running, monitor for self-diagnostic codes. Use test results to identify a faulty component or circuit.