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Basic Inspection: G20

NOTE: Use the following procedure to check and adjust throttle position switch, ignition timing and idle speed. Ensure no Diagnostic Trouble Codes (DTCs) exist before performing test. See SELF-DIAGNOSTICS - G20 article. Ensure transmission is in Park or Neutral, all electrical accessories (headlights, A/C, rear window defogger, cooling fan, etc.) are turned off and steering wheel is in straight-ahead position.
  1. Check the following:
    • Harness connectors for poor connections.
    • Vacuum hoses for leaks, kinks or misrouting.
    • Wiring for improper connections, pinches and cuts.
    • Air filter for clogging.
    • Air intake duct for leaks.

    Repair as necessary. Go to next step.

  2. Check for clearance between throttle drum and throttle stop. See Fig 1. If clearance exists, go to next step. If clearance does not exist, check for loose throttle opener mounting bolts. Tighten if necessary. If bolts are not loose, repair or replace throttle body assembly as necessary. Go to next step.
  3. Start engine and let it idle. Throttle opener rod should move backward and clearance should exist between throttle drum and throttle opener rod. See Fig 1. If throttle opener operates as specified, go to step  5. If throttle opener does not operate as specified, go to next step.
  4. With engine idling, check for vacuum at throttle opener vacuum hose. If vacuum exists, repair or replace throttle body assembly. If vacuum does not exist, repair or replace vacuum hose. Go to next step.
  5. If throttle drum is contacting throttle stop, go to step  7. If throttle drum is not contacting throttle stop, turn ignition off. Check for slack in throttle cable. If slack exists, go to next step. If slack does not exist, adjust throttle cable. Go to next step.
  6. Remove air intake duct. Observe throttle valve while operating throttle drum by hand. If throttle valve operation is okay, retighten throttle drum mounting nuts. Go to next step. If throttle valve operation is not okay, clean throttle valve and throttle body. Go to next step.
  7. Reinstall air intake duct. Start engine and warm to normal operating temperature. Turn ignition off. Disconnect vacuum hose from throttle opener. Using a hand vacuum pump, apply vacuum to throttle opener until throttle drum is not contacting throttle opener rod. See Fig 1. Go to next step.
  8. Disconnect Throttle Position (TP) switch harness connector. See Fig 2. Check continuity between TP switch terminals No. 4 and 5, with specified feeler gauges inserted between throttle drum and throttle stop. See Fig 3. See FEELER GAUGE THICKNESS  table. If continuity is as specified, go to step  12. If continuity is not as specified, go to next step.
  9. Loosen TP sensor mounting bolts. Ensure throttle drum is not contacting throttle opener rod. See Fig 1. Insert.002" (.05 mm) feeler gauge between throttle drum and throttle stop. Rotate TP sensor counterclockwise until continuity does not exist.
  10. Slowly rotate TP sensor clockwise until continuity exists. Temporarily tighten TP sensor bolts. Open and close throttle a few times to verify that continuity does not exist when throttle is open and exists when throttle is closed. Go to next step.
  11. Remove.002" (.05 mm) feeler gauge and insert.006" (.16 mm) feeler gauge. Open and close throttle a few times to verify that continuity does not exist when throttle is closed. Tighten TP sensor mounting bolts and retest. If adjustment is okay, go to next step.
  12. Ensure throttle drum is not contacting throttle opener rod. See Fig 1. Reconnect TP switch harness connector. Plug throttle opener vacuum hose. Start engine and warm to normal operating temperature. Turn ignition off. Go to next step.
  13. Turn ignition on and wait at least 5 seconds. Turn ignition off and wait at least 5 seconds. Repeat 20 times to reset TP sensor idle position memory. Go to next step.
  14. Turn ignition off. Remove vacuum pump and reinstall vacuum hose to throttle opener. Start engine and warm to normal operating temperature. Turn ignition off. Disconnect TP sensor harness connector. See Fig 2. Start engine. Check ignition timing with a timing light. See BASE IGNITION TIMING  table. Adjust timing by rotating distributor, if necessary. Go to next step.
  15. Turn ignition off. Reconnect TP sensor harness connector. Start engine and let it idle. Check ignition timing again. See BASE IGNITION TIMING  table. If ignition timing is as specified, go to step  20. If ignition timing is not as specified, go to next step.
  16. Perform Idle Air Volume Learning. See FUEL SYSTEM in REMOVAL, OVERHAUL & INSTALLATION article. With TP sensor connected, check ignition timing again. If ignition timing is okay, go to step  20. If ignition timing is not okay, go to next step.
  17. Check vacuum hoses for leaks. If no leaks are found, go to next step. If any leaks are found, repair as necessary. Go to step  16.
  18. Check IACV-AAC valve and circuit. See DTC P0505: IDLE AIR CONTROL VALVE-AUXILIARY AIR CONTROL (IACV-AAC) VALVE under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - G20 article. Repair as necessary. Go to step  16. If no problems are found, go to next step.
  19. Substitute Engine Control Module (ECM) with a known-good unit. Go to step  16.
  20. Start engine andwarm to normal operating temperature. Check idle speed. Idle speed should be 750-850 RPM with transmission in Park or Neutral. If idle speed is as specified, go to step  22. If idle speed is not as specified, go to next step.
  21. Perform Idle Air Volume Learning. See FUEL SYSTEM in REMOVAL, OVERHAUL & INSTALLATION article. Check idle speed again. If idle speed is still not as specified, go to step  17. If idle speed is now as specified, go to next step.
  22. Test is complete. Erase any DTCs in ECM and Transmission Control Module (TCM) that may have been set by performing test.
Fig 1: Checking Throttle Opener Operation (G20)
G00010145Courtesy of NISSAN MOTOR CO., U.S.A.
Fig 2: Locating TP Sensor Harness Connector (G20)
G00010124Courtesy of NISSAN MOTOR CO., U.S.A.
Fig 3: Testing Closed Throttle Position (TP) Switch
G99A51086Courtesy of NISSAN MOTOR CO., U.S.A.
FEELER GAUGE THICKNESS

Application Continuity No Continuity
G20 .002" (.05 mm) .006" (.16 mm)
Q45 .008" (.20 mm) .012" (.30 mm)
BASE IGNITION TIMING

Application (1) Specification
G20 & Q45 13-17° BTDC
(1) Check with transmission in Neutral and no electrical load on engine.
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