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Home >> Mazda >> 2000 >> MX-5 Miata Base, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0300: Random Misfire Detected >> Diagnosis & Repair Procedure
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Diagnosis & Repair Procedure

  1. Ensure FREEZE FRAME PID data has been recorded. Check service bulletins. Go to next step.
  2. Turn ignition on. Verify stored DTCs. If any other DTCs are present, repair those DTC(s) first. If no other DTCs are present, go to next step.
  3. Using scan tool, enter PID/DATA MONITOR AND RECORD. Check PID data with ignition on and at idle for BRK SW, ECT V, IAT V, MAF V, RPM, TP V and VS. Compare readings with specifications. See PIN VOLTAGE/PID VALUE CHARTS article. If all data is within specification, go to next step. If any data is not within specification, go to applicable test in SYSTEM & COMPONENT TESTING - MIATA, MILLENIA, MPV, PROTEGE & 626 article. After repair, go to step  21.
  4. Check PID data for BRK SW, ECT V, IAT V, MAF V, RPM, TP V and VS while operating vehicle for at least 2 minutes under same conditions as when DTC was set. If all data is within specification, go to next step. If any data is not within specification, go to applicable test in SYSTEM & COMPONENT TESTING - MIATA, MILLENIA, MPV, PROTEGE & 626 article. After repair, go to step  21.
  5. Check camshaft position sensor and installation. See BASIC DIAGNOSTIC PROCEDURES article. If sensor and related components are not damaged and installed correctly, go to next step. If problems are present, repair as necessary. Go to step  21.
  6. Check crankshaft position sensor installation. See BASIC DIAGNOSTIC PROCEDURES article. If sensor is tight, go to next step. If sensor is loose, repair as necessary. Go to step  21.
  7. Using a timing light connected to each spark plug wire in turn, start engine and check for stable and regular flashing of timing light. If any spark plug wires do not cause timing light to flash properly, go to next step. If all spark plug wires cause timing light to flash properly, go to step  11.
  8. Check spark plug wires for open circuits and damage. If wires are okay, go to next step. If any spark plug wires are faulty, replace as necessary and go to step  21.
  9. Disconnect ignition coil connector. Turn ignition on. Check voltage at coil harness connector terminal "A" (Black/White wire). If battery voltage is present, go to next step. If battery voltage is not present, repair open circuit between ignition switch and ignition coil. After repair, go to step  21.
  10. Check ignition coil resistance. See BASIC DIAGNOSTIC PROCEDURES article. If coil is okay, go to step  21. If coil is faulty, replace coil and go to step  21.
  11. Start engine. Using scan tool, check MAF V PID while revving engine. If MAF V PID changes quickly, go to next step. If MAF V PID does not change quickly, replace MAF sensor and go to step  21.
  12. Check for vacuum leaks from intake system. If no problem is found, go to next step. If any leak is found, repair as necessary. After repair, go to step  21.
  13. Check fuel line pressure. See BASIC DIAGNOSTIC PROCEDURES article. If line pressure is 53-61 psi (3.7-4.3 kg/cm2 ), go to step  16. If line pressure is less than 53-61 psi (3.7-4.3 kg/cm2 ), go to next step. If fuel pressure is more than 53-61 psi (3.7-4.3 kg/cm2 ), check fuel return line for clogging. If no problem is found, replace fuel pressure regulator. After repair, go to step  21.
  14. Check fuel pump maximum pressure. See BASIC DIAGNOSTIC PROCEDURES article. If maximum pressure is okay, go to next step. If maximum pressure is not okay, repair wiring or replace fuel pump. After repair, go to step  21.
  15. Check for leaks in fuel lines. If any leaks are found, repair as necessary and go to step  21. If no problems are found, check for clogging at fuel filter. If clogging is present, check fuel tank for debris. If fuel tank is okay, replace fuel filter and go to step  21. If fuel tank has debris, clean tank, replace fuel inlet filter (sock) and fuel filter. Go to step  21. If no problems are found, replace pressure regulator and go to step  21.
  16. Check engine compression. If compression is okay, go to next step. If compression is not okay, repair as necessary. Go to step  21.
  17. Turn ignition off. Connect vacuum pump to purge solenoid valve. Apply vacuum. Purge solenoid valve should hold vacuum. Turn ignition on. Using scan tool, select SIMULATION TEST and PRGV PID. Set duty cycle to 100 per cent. Purge solenoid valve should release vacuum. If purge solenoid valve operates as specified, go to next step. If purge solenoid valve does not operate as specified, replace purge solenoid valve. After repair, go to step  21.
  18. Turn ignition off. Check PCV system. If PCV system is okay, go to next step. If problem is found, repair as necessary and go to step  21.
  19. Check EGR system. See applicable test in SYSTEM & COMPONENT TESTING - MIATA, MILLENIA, MPV, PROTEGE & 626 article. If no problems are found, go to next step. If EGR valve is stuck open, replace or repair as necessary. Go to step  21.
  20. Check cooling system for combustion gases. If no problem is found, go to next step. If combustion gases are found in cooling system, repair leak and go to next step.
  21. Connect all connectors. Turn ignition on. Erase DTC. See CLEARING CODES in SELF-DIAGNOSTICS - INTRODUCTION - MIATA, MILLENIA, MPV & PROTEGE article. Start engine. Conduct drive mode No. 1. See DRIVE CYCLE PROCEDURE under SELF-DIAGNOSTICS - INTRODUCTION - MIATA, MILLENIA, MPV & PROTEGE article. If DTC P0300 is not present, go to next step. If DTC P0300 is present in PENDING TROUBLE CODE information, replace PCM. Go to next step.
  22. Erase DTC. See CLEARING CODES in SELF-DIAGNOSTICS - INTRODUCTION - MIATA, MILLENIA, MPV & PROTEGE article. Verify if any DTCs are stored or are present in PENDING TROUBLE CODE information. If no DTCs are present, testing is complete. If any DTCs are present, go to applicable test and repair.
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