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DTC P0300: Random Misfire Detected: Testing

NOTE: Ensure freeze frame data has been recorded. Check for service bulletins and on-line information.
  1. If any other DTCs are present, repair those DTC(s) first. If no other DTCs are present, go to next step.
  2. Using scan tool, access PID/DATA MONITOR. Record PID data for RPM, TP V, ECT V, IAT V, MAF V, BRK SW and VS with ignition switch on and engine idling. Compare readings with specifications. See PIN VOLTAGE/PID VALUE CHARTS article. 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  20 . If all data is within specification, go to next step.
  3. Referring to FREEZE FRAME PID data, operate vehicle under same conditions as when DTC was set. Record PID data for RPM, TP V, ECT V, IAT V, MAF V, BRK SW 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  20 .
  4. Check CMP sensor installation. Check CMP sensor. See SYSTEM & COMPONENT TESTING - MIATA, MILLENIA, MPV, PROTEGE & 626 article. Check related components, including timing belt and gears. If no problem is found, go to next step. If any problem is found, repair as necessary. After repair, go to step  20 .
  5. Start engine. Using an inductive timing light, check for steady flashing from each spark plug wire. If any wire does not cause steady flashing, go to next step. If all wires check okay, go to step  9 .
  6. Turn ignition off. Check suspect spark plug wire. If wire is okay, go to next step. If wire is faulty, replace wire. After repair, go to step  20 .
  7. Disconnect ignition coil connector. Turn ignition on. Check voltage between harness connector terminal "D" (Green/Black wire) and ground. If battery voltage is present, go to next step. If battery voltage is not present, repair open on circuit between connector and ignition switch. After repair, go to step  20 .
  8. Check ignition coil resistance. See BASIC DIAGNOSTIC PROCEDURES article. If coil is okay, go to next step. If coil is faulty, replace coil. After repair, go to step  20 .
  9. Start engine. Using scan tool, monitor MAF V PID. Depress accelerator pedal to WOT and release to race engine. Scan tool should display MAF sensor changes equal to RPM changes. If voltage is as specified, go to next step. If voltage is not as specified, replace MAF sensor. After repair, go to step  20 .
  10. Check for vacuum leaks. If no leaks are found, go to next step. If any leaks are found, repair as necessary. After repair, go to step  20 .
  11. Check fuel pressure with engine at idle. See BASIC DIAGNOSTIC PROCEDURES article. If pressure is more than 45-51 psi, go to next step. If pressure is 45-51 psi, go to step  15 . If pressure is less than 45-51 psi, go to step  13 .
  12. Disconnect vacuum line from fuel pressure regulator. Check for vacuum at disconnected line. If vacuum is present, check fuel pump maximum pressure. See BASIC DIAGNOSTIC PROCEDURES article. Check return line for clogging. If problem is found, repair as necessary. If no problem is found, replace fuel pressure regulator. After repairs, go to step  20 . If no vacuum is present, check vacuum line routing. If problem is found, repair as necessary. If vacuum routing is okay, replace PRC solenoid. After repairs, go to step  20 .
  13. Turn ignition off. Check fuel system maximum pressure. See BASIC DIAGNOSTIC PROCEDURES article. If fuel pressure is 86-110 psi, go to next step. If fuel pressure is not 86-110 psi, check fuel pump circuit. If problem is found, repair as necessary. If no problem is present, replace fuel pump. After repair, go to step  20 .
  14. Check fuel system for leaks. If any leaks are found, repair as necessary and go to step  20 . If no leaks are found, check fuel pump pickup screen and fuel filter. Replace as necessary. If no problems are found, replace fuel pressure regulator. After repair, go to step  20 .
  15. Check engine compression. If compression is okay, go to next step. If compression is low, repair as necessary. After repair, go to step  20 .
  16. Turn ignition off. Connect vacuum pump to purge control solenoid valve. Apply vacuum. Valve should hold vacuum. Turn ignition on. Using scan tool, select PRGV PID in SIMULATION TEST. Set duty cycle to 100 percent. Apply vacuum while turning valve on and off. Valve should release vacuum when turned on. If valve operates as specified, go to next step. If valve does not operate as specified, replace purge control solenoid valve. After repair, go to step  20 .
  17. Check PCV valve operation. See SYSTEM & COMPONENT TESTING - MIATA, MILLENIA, MPV, PROTEGE & 626 article. If PCV is okay, go to next step. If PCV is faulty, repair or replace as necessary. After repair, go to step  20 .
  18. Check EGR valve operation. See SYSTEM & COMPONENT TESTING - MIATA, MILLENIA, MPV, PROTEGE & 626 article. If EGR valve is okay, go to next step. If EGR valve is faulty or stuck open, repair or replace as necessary. After repair, go to step  20 .
  19. Check cooling system for combustion gasses. If no combustion gasses are present, go to next step. If combustion gasses are present, repair leak as necessary. After repair, go to next step.
  20. Erase DTC. See CLEARING CODES in SELF-DIAGNOSTICS - INTRODUCTION - MIATA, MILLENIA, MPV & PROTEGE article. Conduct Drive Mode No. 1 under DRIVE CYCLE PROCEDURE. See SELF-DIAGNOSTICS - INTRODUCTION - MIATA, MILLENIA, MPV & PROTEGE article. Verify if DTC P0300 is present in PENDING TROUBLE CODE information. If DTC is present, replace PCM and go to next step. PCM is mounted to passenger floor, behind glove box. If DTC is not present, go to next step.
  21. Perform after repair procedure. See AFTER REPAIR PROCEDURE  . If no DTC is present, testing is complete. If any DTC is present, go to appropriate test for diagnosis and repair.
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