Diagnostic Aids

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

• IAC system.
• MAP system.
• EGR system.

To prevent replacing good components, be aware the following non-EEC-IV areas may be at fault:

• Faulty power or ground connections.
• Secondary ignition (distributor cap, rotor, wires, coil and plugs).
• Engine mechanical components (compression, timing, valves, etc.).

1. Step 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. Step 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 next step. If RPM does not drop, CIRCUIT TEST KE, step 4).
3. Step 3) Power To MAP Sensor  Turn ignition off. Disconnect MAP sensor. Connect MAP tester between wiring harness and MAP sensor. See Fig 1 . Connect banana plugs of tester into DVOM. Turn ignition on. If Green light is on, go to next step. If Green light is off, repair open VREF circuit and check system operation.
   Fig 1: MAP Tester & Circuit

   
4. Step 4) MAP Tester Output Reading  If possible, measure several known-good MAP sensors to obtain average voltage for location and day of testing. With MAP tester and DVOM connected, turn ignition on. Measure MAP voltage at MAP sensor. If voltage is not within specification for specific altitude, replace MAP sensor. See MAP VOLTAGE OUTPUT  table. If voltage is in within specification for specific altitude, go to next step.
   MAP VOLTAGE OUTPUT
   
   

   Approximate Elevation (Ft.)	Voltage Output (Volts)
   0	1.55-1.63
   1000	1.52-1.60
   2000	1.49-1.57
   3000	1.46-1.54
   4000	1.43-1.51
   5000	1.40-1.48
   6000	1.37-1.45
   7000	1.35-1.43

5. Step 5) Check Vacuum Lines  Check vacuum hoses for correct routing. Refer to VECI decal. Check MAP sensor vacuum hose for leaks and blockage. If vacuum hoses are okay, go to next step. If vacuum hoses are not okay, repair as necessary. Repeat QUICK TEST  .
6. Step 6) Check MAP Sensor  Turn ignition off. Disconnect vacuum hose from manifold vacuum source. Connect vacuum pump to MAP sensor hose. Apply 18 in. Hg vacuum to MAP sensor. If MAP sensor holds vacuum, go to next step. If MAP sensor does not hold vacuum, replace MAP sensor or hose and repeat QUICK TEST  .
7. Step 7) Check Vacuum Manifold Source  Install vacuum gauge at manifold vacuum source. Start engine and observe vacuum gauge. If manifold vacuum is present, remove vacuum gauge. Reconnect MAP sensor vacuum hose, and go to next step. If vacuum is not present, remove obstruction and repeat QUICK TEST  .
8. Step 8) Check EGR Vacuum  If vehicle is not equipped with EGR system, go to CIRCUIT TEST H, step 2). Disconnect and plug vacuum line at EGR valve. Attempt to start engine. If vehicle did not start previously but starts now or if driveability symptoms are eliminated, go to CIRCUIT TEST DN, step 42). If vehicle could not start previously and still does not start or if vehicle driveability fault is still present, go to next step.
9. Step 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.