Diagnostic Aids

Perform this test only when directed by CIRCUIT TEST AA, CIRCUIT TEST AB or CIRCUIT TEST AC  . This test is intended to diagnose:

• IAC system.
• EGR system.

1. 1) IAC Check
   
   Try to start engine at part throttle. If engine starts and runs smoothly at part throttle, go to CIRCUIT TEST KE  , step 4). If engine does not run as described, go to step 3). If engine starts and idles smoothly, go to next step.
2. 2) Check For RPM Drop
   
   Turn ignition off. Connect a tachometer to engine. Start engine. Disconnect IAC solenoid. If RPM drops or engine stalls, reconnect IAC solenoid and go to step 8). If RPM does not drop, CIRCUIT TEST KE  , step 4).
   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 2) to step 8). No test procedures have been omitted.
3. 8) Check EGR Vacuum
   
   If vehicle is not equipped with EGR system, go to CIRCUIT TEST H, step 2). If vehicle is equipped with EGR, disconnect and plug vacuum line at EGR valve. Attempt to start engine. If vehicle could not start previously and still does not start or if vehicle driveability fault is still present, go to next step. If vehicle did not start previously but starts now or if driveability symptoms are eliminated, go to one of the following:
   • Models with Differential Pressure Feedback EGR (DPFE), go to CIRCUIT TEST DL  , step 50).
   • Models with Pressure Feedback EGR (PFE), go to CIRCUIT TEST DL  , step 21).
   • On all other models, go to CIRCUIT TEST DN  , step 42).
4. 9) Check EGR Valve
   
   Inspect EGR valve for leaks. If valve is fully closed, go to CIRCUIT TEST H  , step 2). If EGR valve is leaking or is not fully seated, repair or replace valve as necessary.