Engine Performance - Rough or Incorrect Idle Speed
88cad03Bulletin No.: T-88-112
File in Group: 6E
Number: 58
Corp. Ref.No.: 836514
Date: April '88
SUBJECT: ROUGH, UNSTABLE OR INCORRECT IDLE, AND/OR STALLING AT IDLE
MODELS AFFECTED: 1988 CIMRRONS
The following service information revises the recommended diagnostic procedure referenced on page 6E3-B-7 of the 1988 Service Information Manual.
Some 1988 Cimarrons may experience a condition of rough, unstable or incorrect idle speed, and/or stalling at idle.
This condition may be caused by a loss of idle air control valve (IACV) position at which the engine idles. During normal vehicle operation the ECM learns the correct position for the IACV to maintain proper engine idle speed. Each vehicle will have a unique value, depending on the throttle body base air rate setting, deposit buildup, etc. This information is retained in the ECM's "keep alive" memory. If the ECM is without battery power for any reason, then the IACV position information for stable engine idle is "lost" and replaced with a default value.
To repair this condition, perform the following procedure:
1. Restore the battery power and place air conditioning controls in the off position.
2. Start the engine and shift the transmission to "drive" for automatics or "neutral" for manuals.
3. Allow the engine to run approximately five minutes until the normal operating temperature is attained.
4. After attaining operating temperature, allow the engine to idle for an additional two minutes.
This procedure will allow the ECM memory to be updated with the correct IACV position for the vehicle providing a stable idle rpm.