Service Procedure

1. Allow the vehicle to sit a minimum of 8 hours.

2. Use New Generation Star (NGS) Tester to monitor engine rpm during the concern.

3. Before starting the vehicle, turn the climate control system to defrost, headlights to the high beam position, and rear defroster on.

4. If engine speed drops below 400-600 rpm within the first 15 seconds after start, or engine becomes rough or stalls, perform the following procedure: Run NGS or Service Bay Diagnostic System (SBDS) to determine if there are any Diagnostic Trouble Codes (DTCs) in system.

5. Service all hard fault codes first (if present).

6. If you have any of the following memory codes, P0131, P0132, P0133 and P0135, refer to the Powertrain Control/Emissions Diagnosis (PC/ED) Service Manual Pinpoint Test H to diagnose these codes before proceeding.

7. If DTCs P0171 or P0172 are present, check the air induction system for air leaks or blockages according to PC/ED Service Manual Pinpoint Test HU.

NOTE
DO NOT REPLACE THE HEATED EXHAUST GAS OXYGEN (HEGO) SENSORS FOR CODES POl7l OR P0172 WITHOUT ANY HEGO CODES. THESE CODES MAY BE CAUSED BY OTHER MALFUNCTIONING COMPONENTS AND DO NOT INDICATE A DEFECTIVE HEGO SENSOR.

8. At idle, vehicle in NEUTRAL under normal operating temperature and with all accessories OFF, check the following:

a. Barometric pressure reading should be within +/- 8 Hz of the normal reading for your altitude. Determine the normal barometric pressure for your altitude by referring to the SBDS cart or by using NGS Tester to measure several good vehicles which have been driven that day.

b. MAF voltage should be no greater than 0.70 volts.

c. Long term fuel trim (NGS PID "LONGTI") should not exceed negative 12% (i.e., -13% is out of limit).

If two or more of the above readings are not within the specified range, install new MAF Sensor (F5RZ-12B579-B). If only one parameter is not within the specified range or if there are any other codes in the system, proceed to the PC/ED Service Manual for further diagnosis.

NOTE
ONLY MAF SENSORS WITH DATE CODE 8A15 OR AFTER SHOULD BE INSTALLED, 8=1998, A=JANUARY, 15=DAY OF MONTH.

NOTE
THE BARO (BAROMETRIC PRESSURE) VALUE DISPLAYED ON THE NGS/SBDS IS INFERRED BY THE PCM. THE PCM CONSIDERS MANY EEC INPUT SIGNALS INCLUDING RPM, MAF AND TP TO INFER LOCAL BAROMETRIC PRESSURE. THEREFORE, AFTER THE MAF SENSOR IS REPLACED, THE INFERRED BARO READING WILL NOT CHANGE UNTIL THE VEHICLE IS DRIVEN LONG ENOUGH TO ALLOW THE ADAPTIVE STRATEGY TO RELEARN.

NOTE
DO NOT ATTEMPT TO CLEAN THE MAF SENSOR. CLEANING THE MAF SENSOR WILL NOT RESOLVE THE CONCERN AND MAY DAMAGE THE SENSOR ELEMENT.

9. Locate the correct replacement part number from the PCM Application Chart provided in this article.

^ 1995 Model Year - Replace the PCM

^ 1996 and 1997 Model Years - Reprogram the PCM

NOTE
DO NOT REFER TO OASIS OR THE ON-VEHICLE CALIBRATION LABEL TO DETERMINE THE REPLACEMENT PCM PART NUMBER. PREVIOUS SERVICE ACTIONS MAY HAVE UPDATED THE ORIGINAL CALIBRATION. FAILURE TO FOLLOW THIS IDENTIFICATION PROCEDURE MAY RESULT IN DRIVEABILITY CONCERNS.

NOTE
DO NOT REMOVE OR COVER PREVIOUSLY INSTALLED AUTHORIZED MODIFICATION DECALS.

NOTE
FOR 1995 MODEL YEAR, THE PCMs MUST BE REPLACED. THEY CANNOT BE REPROGRAMMED. FOR 1996 AND 1997 MODEL YEARS, PCM REPLACEMENT IS NOT AUTHORIZED BY THIS TSB. REFER TO THE POWERTRAIN CONTROL/EMISSIONS DIAGNOSIS (PC/ED) SERVICE MANUAL FOR APPROPRIATE DIAGNOSTIC PROCEDURES IF PCM HARDWARE CONCERNS EXIST.

NOTE
IF YOU ENCOUNTER DIFFICULTIES WHEN REPROGRAMMING, REFER TO TSB 97-9-8 FOR DETAILED INSTRUCTIONS. PCMs SHOULD ONLY BE REPLACED WHEN THEY CAN NO LONGER BE REPROGRAMMED OR THEY ARE DAMAGED.





Obtain an Authorized Modifications Decal (FPS 8262 - obtainable through DOES II, 25/pkg) and list the date, dealer number, and summary of modifications performed. Select a prominent place adjacent to the Vehicle Emission Control Information Decal suitable for installing the Authorized Modifications Decal. Clean the area, install the decal, and cover it with a clear plastic decal shield.