ECU - Low Idle Speed Vibration

89AMCjeep03

Models


1987-1989 MJ, XJ, & YJ Body With 2.5L Engine


Subject


Low Idle Speed Vibration


Index

DRIVEABILITY


Date

March 20, 1989


No.

18-51-89

P-1187 (C18-53)
BODY CODE LEGEND

MJ - COMANCHE XJ - CHEROKEE AND WAGONEER YJ - WRANGLER


SYMPTOM/CONDITION

Some 1987-1989 Jeep vehicles equipped with the 2.5L engine may exhibit a vibration at low idle speed. This condition will be most noticeable once the engine has reached its normal operating temperature.

This vibration condition can be improved by installing an idle speed jumper harness in the ECU circuit. This will increase the idle RPM by changing the idle mode signal to the ECU.

DIAGNOSIS

Allow the engine to reach normal operating temperature. Connect a tachometer to the engine ignition. Set the parking brake and place the transmission in neutral. Start the engine and verify that the engine is at idle and above a minimum of 750 RPM. Using the accelerator, raise the engine idle to 950 RPM. If the vibration complaint is now satisfied, then proceed with the following repair procedure.

If the initial idle speed is below 750 RPM or the vibration complaint is not satisfied at 950 RPM, the cause must be determined prior to performing this repair procedure. Determine the cause by performing a vehicle test with the DRB II or the MS 1700 Tester, and by visual inspection of components, such as vacuum hoses and connections, powertrain mounting and exhaust system.
PARTS REQUIRED

Idle Speed Harness

1987-89 2.5L Wrangler P/N 56002-101

1987-89 2.5L Cherokee, P/N 83100-070
Wagoneer, Comanche

FIGURE 1:

FIGURE 2:

REPAIR PROCEDURES

1. Locate the Electronic Engine Control (EEC) Harness Connector (A) under hood. The connector can be found on the right wheel well near the fuel pump and B+ latch relays on Cherokee, Wagoneer and Comanche models, and between the battery and charcoal canister on Wrangler models.
NOTE: FOR THE WRANGLER, THE CONNECTOR (A) WILL BE A 4 TERMINAL CONNECTOR (FIGURE 1). THE CONNECTOR (A) FOR THE CHEROKEE, WAGONEER AND COMANCHE WILL BE A 6 TERMINAL CONNECTOR (FIGURE 2).

FIGURE 3:

FIGURE 4:

2. Disconnect the EEC Connector and install the idle speed jumper harness
(B) between the EEC harness connector. Figure 3 shows the Wrangler with idle jumper harness installed. Figure 4 shows the Cherokee, Wagoneer, and Comanche with idle jumper harness installed.

3. Recheck the idle speed using a tachometer and verify that it is 950 +/- 50 RPM.

4. Remove the tachometer.

NOTE: THE IDLE SPEED JUMPER HARNESS HAS THE SAME EFFECT ON VEHICLES EQUIPPED WITH OR WITHOUT AIR CONDITIONING. THE JUMPER HARNESS CAUSES AN INCREASE IN IDLE SPEED BY SENDING A STEP-UP SIGNAL TO THE ECU THAT SIMULATES FULL-TIME AIR CONDITIONING OPERATION. THE LOW IDLE SPEED JUMPER HARNESS SHOULD BE REMOVED FROM THE EEC HARNESS PRIOR TO TESTING THE VEHICLE WITH THE DRB II OR THE MS 1700 TESTER TO PREVENT INVALID TESTS.
POLICY: Reimbursable within the provisions of the warranty.


TIME ALLOWANCE:
Labor Operation No. 08-90-65-91 . . . . . . . . . . 0.3 Hrs.


FAILURE CODE: 15 - Calibration