ECM - Idle Speed Dips Below Specified Rpm
90chrysler12 NO.: 18-26-90GROUP: DRIVEABILITY
DATE: Oct. 22, 1990
SUBJECT: Closed Throttle Idle Undershoot During Deceleration 3.9L/ 5.2L/5.9L Engines
MODELS: 1990 (AB) RAM VAN/WAGON (RWD) (AD) RAM PICKUP/RAM CAB & CHASSIS/RAMCHARGER POWER RAM CAB & CHASSIS (4WD) (AN) DAKOTA/DAKOTA SPORT/DAKOTA CONVERTIBLE DAKOTA CAB & CHASSIS
SYMPTOM/CONDITION
Some vehicles may exhibit an "idle undershoot" condition during closed throttle deceleration. "Idle undershoot" occurs when engine RPM dips below specified idle RPM and results in a complaint of idle roughness. An idle speed increase may also occur due to system overcorrection. This condition will most likely occur only after engine has reached normal operation temperature.
DIAGNOSIS
Using a DRB II tester and the 1990 Powertrain Diagnostic manual for 3.9/5.2/5.9L EFI (Publication #81-699-0025), verify that all vehicle systems are functioning as designed. Be sure to check minimum idle air flow. If all systems are functioning correctly, proceed with the following diagnosis.
Condition may be diagnosed during a road test using low speed driving (highway speeds are not required). Release the throttle pedal completely. Engine RPM will drop below the specified idle then back to the correct idle RPM. Test may need to be performed several times before condition can be duplicated.
If the condition occurs, perform the following procedure.
PARTS REQUIRED
1 Single Module Engine Controller (SMEC)
AN Truck
AB Van/Wagon
AD Ram Pickup/Ramcharger
1 Authorized Modification Label PN 4275086
REPAIR PROCEDURE
This repair involves the replacement of the original engine controller with a revised unit.
1. Replace the engine controller (SMEC/SBEC) with the appropriate unit as called out in PARTS REQUIRED.
Figure 1:
2. Type the required information on the Authorized Modification Label, as illustrated in Figure 1, and attach near the VECI label.
*INSERT PART NUMBER USED
POLICY: Reimbursable within the provisions of the warranty.
TIME ALLOWANCE:
Labor Operation No. 08-19-90-91 . . . . . . . . . . . . . . . . . . 0.4 Hrs.
FAILURE CODE: AM - Authorized Modification