Engine Idles Rough and/or Misses

1. Access diagnosis codes. If abnormal codes are present, proceed to ``Diagnosis Code Interpretation.'' If a normal code is present, proceed to step 2.
2. Check for vacuum leaks in air intake line. If no vacuum leaks are present, proceed to step 3. If vacuum leaks are present, check the following:
a. Hose connections.
b. PCV hoses.
c. Ensure EGR valve stays open.
d. Oil filler cap and oil level gauge.
3. Check air filter. If air filter is satisfactory, proceed to step 4. If air filter is not satisfactory, replace air filter.
4. Check curb idle speed. If idle speed is satisfactory, proceed to step 5. If idle speed is not satisfactory, adjust as required.
5. Check ignition timing. If timing is satisfactory, proceed to step 6. If timing is not satisfactory, adjust as required.
6. Ensure spark plugs are satisfactory. If plugs are satisfactory, proceed to step 7. If plugs are not satisfactory, replace plugs as required and check compression pressure.
7. On models so equipped with idle air control valve, ensure air control valve is closed. If air control valve is closed, proceed to step 8. If air control valve is open, check vacuum solenoid valve and vacuum lines for leaks.
8. On all models, check cold start injector for proper operation. If injector is satisfactory, proceed to step 9. If injector is not satisfactory, replace cold start injector and/or start injector time switch.
9. Ensure fuel pressure is as specified. If fuel pressure is satisfactory, proceed to step 10. If fuel pressure is not satisfactory, check the following:
a. Fuel pump.
b. Fuel filter.
c. Fuel pressure regulator.
10. Check fuel injectors for proper operation. If injectors are satisfactory, proceed to step 11. If injectors are not satisfactory, repair or replace as required.
11. Ensure EFI electronic circuit is satisfactory. If circuit is satisfactory, test is complete. If circuit is not satisfactory, check the following:
a. Fusible link, fuse or EFI main relay.
b. Air flow meter.
c. Water thermo sensor.
d. Injection signal circuit.
e. Air temperature sensor (if equipped).
f. Oxygen sensor.