Malibu V6-191 3.1L VIN M SFI (1997)
Idle Speed: Customer Interest
PROM - Unstable Engine Idle
File In Section: 6E - Engine Fuel & Emission
Bulletin No.: 77-65-17
Date: July, 1997
Subject:
Unstable Engine Idle (Reprogram PCM)
Models:
1997 Chevrolet Malibu
1997 Oldsmobile Cutlass
with 3100 V6 Engine (VIN M - RPO L82)
Condition
Some owners may experience an unstable engine idle. The controlled engine idle may vary approximately 50 RPM from desired idle. This typically
occurs during an extended idle period beyond 30 seconds with the transmission in park or neutral and the air conditioning turned off.
Cause
The Pre Converter Heated Oxygen Sensor (HO2S1) voltage output is driven low and holds there (lean). The Post Converter Heated Oxygen Sensor
(HO2s2) voltage output will hold then at a high voltage (rich). This can drive one sensor to cancel out the other thus not allowing fuel trim or the Post
Converter Heated Oxygen Sensor can take over fuel trim control. If the Post Converter Heated Oxygen takes over fuel trim control, the system thinks it is
running rich and the Long Term Fuel Trim will make adjustments to lean the system. Either of these conditions will cause a rolling or hunting idle.
Correction
Check the calibration identification number utilizing a scan tool device. Re-flash with the updated calibration if the current calibration is not one listed in
this bulletin. If the vehicle already has the most recent calibration, then refer to the appropriate service repair manual to diagnose and repair. Test drive
the vehicle after repair to ensure that the condition has been corrected. The new calibrations are available from the GM Service Technology Group
starting with CD number 12 for 1997.
Important:
There are three methods for programming a PCM
1.
Direct Programming. The vehicle is directly connected via the Data Link Connector (DLC) on the Dealers/Retailers Techline equipment. (T-20
Plus, T-50 and T-60 only) Vehicle must be present.
2.
Remote programming. The new program is downloaded into the Dealers/Retailers scan tool and then downloaded into the vehicle from the scan
tool via the DLC. Tech 2 required. Vehicle must be present.
3.
Off-Car Programming. A PCM may be programmed while removed from the vehicle by using the off-board programming adapter (OBPA), P/N
41207-B. This adapter can be connected to either the Techline Terminal for direct programming or the scan tool for remote programming. Not
necessary for the vehicle to be present.
Refer to the appropriate Service Manual or Techline Information for more detailed instructions.
Parts Information
Part Number
Carline
Emission
16266904
Malibu, Cutlass
USA Nationwide
16266914
Malibu, Cutlass
Canadian/Unleaded
Export
16266924
Malibu
Leaded Export
Important:
Do not attempt to order the calibrations from GMSPO. The calibrations are programmed into the vehicle's PCM via a Techline Tool device.
Warranty Information
