I just noticed that there is a TSB for code 15 that might have something to do with our problem. I have not ruled out the distributor, but we should check this first. Apparently there have been some issues with the grounding on some of the wiring. Here is the TSB Info:
Some 1990 & 1991 Excel and 1991 Scoupe models may experience recurrent activation of the "Check Engine" light and setting of fault code 15 in the engine control module (ECM) memory. The vehicle may exhibit stalling at idle and an inoperative air conditioning compressor when this condition occurs.
These symptoms may be related to a poor throttle position (TP) sensor ground circuit in the ECM wiring harness. The field fix procedure for this condition varies according to the wiring harness manufacturer, but basically involves the soldering of a crimp connection.
The connection involved is located where four black ground wires (five in California specification cars) for the throttle position (TP) sensor, idle speed control (ISC) motor position sensor, volume airflow (VAF) sensor, and engine coolant temperature (ECT) sensor (plus the EGR temperature sensor on California spec. vehicles) are joined with two ground wires leading to the ECM. (See splice SCO8 on page 23-3 of the 1990-1992 Excel Electrical Troubleshooting Manual, or splice SCO3 on page 23-3 of the 1991-1992 Scoupe Electrical Troubleshooting Manual.)
|1. ||Disconnect the battery ground cable. |
|2. ||Under the crash pad on the drivers side, disconnect the ECM wiring harness connectors and ground wires from the ECM. Disconnect the two main wiring harness connectors. Remove the tie strap from around the ECM wiring harness and main wiring harness. |
|3. ||In the engine compartment, disconnect the A/C low pressure switch connector, A/C compressor bullet connector (blue to red wire), distributor connector, purge control solenoid valve connector, EGR control solenoid valve connector (California spec. vehicles only), pre-excitation resistor connector, and the ground wires leading to the firewall (G07 for Excel, G06 for Scoupe). Remove the three bolts attaching the square ECM wiring loom cover to the intake manifold surge tank. Remove the tie strap holding the EGR/purge control solenoid valve wiring to the accelerator cable. |
|4. ||Carefully feed the ECM wiring harness under the crash pad and through the firewall grommet opening into the engine compartment. Pull the harness completely into the engine compartment.|
5. The TP Sensor crimp connection splice is located approximately 8 inches from the firewall grommet on the ECM end of the harness.
6. Peel open the wiring harness cover to find the splice. Remove any electrical tape or shrink wrap tubing overthe splice.
|7. ||Solder the crimp connector following the techniques listed under Soldering Techniques. |
|8. ||Retape the connection using black electrical tape. Rewrap the wiring bundle with the original cover. |
|9. ||Reinstall the wiring harness in its original position. Reattach the square ECM wiring loom cover to the intake manifold surge tank. Reconnect the electrical connectors that were disconnected in steps 2 and 3 and replace the tie straps that were removed. Reconnect the battery ground cable. |
|10. ||Verify that ail wiring harnesses are clear of moving parts or hot components. |
|11. ||Clean off throttle body carbon deposits per procedure given in fuel system section of the appropriate shop manual. Clean TP sensor connectors at throttle body by disconnecting and spraying with electrical contact cleaner. |
|12. ||Using the M.U.T., set the idle speed and TP sensor voltage according to the procedures given in the fuel system section of the appropriate shop manual. |
TP Sensor = 480 - 520 mV
IDLE SPEED = 750 RPM
MP Sensor = 900 - 1000 mV