Bulletin No.: PI0920A
Date: Jul-2013

Subject:

Diagnostic Tips for Intermittent Rough Idle Concern

Models:

2013 Cadillac ATS
2013 Chevrolet Malibu
Equipped with 2.5L Engine (RPO LCV) and 2.0L Engine (RPO LTG)

This PI has been revised to add a Recommendation/Instructions section for ATS and update/add Labor Operations to the
Global Labor Code (GLC). Please discard PI0920.

Condition/Concern
Some customers may experience a rough idle at different points in a drive cycle. This concern is fairly intermittent and there may or may not be any DTCs set on
the vehicle. The service advisor needs to get an accurate description of when it happened. They should also ask about the drive cycle right before the event
occurred.
Here is a list of questions that should help define the concern:

•

When did you notice the rough idle and how long had the vehicle been running before the rough idle?

•

Did they start this drive from an overnight soak, or after a short cold soak/ short hot soak (like after a quick stop at a store)?

•

How long was the soak period (how long did it sit with engine off before the car was started again and the condition occurred)?

•

Did the customer do anything to make the roughness go away? (For example, turn engine off and on, bring it off idle, then let it idle, drive away and then
the next idle the roughness is gone).

There may be several reasons for this rough idle feel that the customer is experiencing and the root cause(s) is under investigation.

Recommendation/Instructions (Malibu)
If there are any DTCs set, record them and follow published diagnostics for the DTC(s) first. If the rough idle is not resolved, drive the vehicle using the same
drive cycle identified by the owner and see if rough idle can be reproduced. Have the GDS snapshot of the engine data ready for this test drive. If the vehicle
does idle rough, several areas to look at include:
–

ECM system voltage – wide swing of system voltage

–

Pre O2 sensor readings were they swinging or staying flat, rich/lean?

–

Long term and short term fuel readings when the event happened.

–

Commanded vs actual fuel pressure reading, too much variance to what the system is requesting.

–

Commanded vs actual intake and exhaust camshaft reading.

–

Engine load rough idle compared to regular idle - abnormal engine loads.

If nothing is found in the engine operation that could be a cause of the rough idle, compare it to another vehicle. A good reference point is the air duct as it runs
across the back of the engine. Does it vibrate excessively compared to another vehicle? If it does, the engine mounts should be neutralized. Refer to Powertrain
Mount Balancing in SI.
Re-evaluate the vehicle idle quality. If the above information does not resolve the rough idle, please contact GM Technical Assistance Center (TAC) for
assistance.

Recommendation/Instructions (ATS)

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There is a revised ECM calibration for the rough idle concern. The revised calibration is available for both 2.0L RPO LTG and 2.5L RPO LCV engines. This
revised calibration should be installed in the vehicle and evaluated.
If the above information does not resolve the rough idle, please contact GM Technical Assistance Center (TAC) for assistance.

Warranty Information
For vehicles repaired under warranty, use:
Labor Operation

Description

Labor Time

4080118*

Balance Procedure – Powertrain Mounts (Malibu Only)

0.5 hr

2810075

Engine Control Module Reprogramming with SPS

Use Published Labor
Operation Time

(ATS Only)
*This is a unique labor operation for bulletin use only. It will not be published in the Labor Time Guide.

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may
occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools,
safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that
your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.

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