| Subject: | Rough Idle While in Gear |
| Models: | 2013-2015 Cadillac ATS |
| 2014-2015 Cadillac CTS | |
| 2015 Chevrolet Colorado | |
| 2015 GMC Canyon | |
| Equipped with 2.5L (RPO LCV) or 2.0L (RPO LTG) 4 Cylinder Engine |
Rough idle while vehicle is in gear.
Note: The roughness is usually felt in the seat/floor pan area, and not in the steering wheel.
The roughness may be described to dissipate during the rise of engine RPMs.
This may be caused by fluid coupling within the transmission torque converter.
If you encounter a vehicle with the above concern, follow the procedure below:
Important: (2013-2014 Cadillac ATS Only) Before proceeding, verify that the latest version of “Rough Idle Concern” has been completed.
- Bring the vehicle up to operating temperature.
- Using a Pico Oscilloscope Diagnostic Kit, mount the PicoScope single-axis or 3 axis vibration sensor (TA143) on the intake cover bolt with the hole on the sensor facing in the forward direction as illustrated above.
Note: Only the use of the Pico Oscilloscope Diagnostic Kit with NVH should be utilized, available from GM Dealer equipment (P/N 733–CH-51450). Previous vibration tools are NOT recommended due to the types and frequencies producing these vibrations.
Important: When using the Pico Oscilloscope Diagnostic Kit, make sure the A/C is not on and vehicle is at idle at all times during testing.
Note: For proper usage of the Pico Oscilloscope Diagnostic Kit, refer to the GM Center of Learning Website for a PicoScope Noise, Vibration, and Harshness Diagnostics Overview.
- Place the vehicle in Neutral, and record a 30 second time frame of the lateral amplitude of engine speed 1 (E1). Be sure to record the findings on the vehicle repair order for reference.
- After recording the vehicle’s lateral amplitude of engine speed 1 with the vehicle in Neutral, repeat a 30 second time frame recording of engine speed 1 lateral amplitude with the vehicle in Drive and in Reverse.
Important: Be sure the brake is applied when attempting recordings while vehicle is in either Drive or Reverse so that there is no movement within the vehicle while recording.
- Once all three of the 30 second recordings of the engine speed 1 lateral amplitude are established, compare the engine speed 1 lateral amplitude of the vehicle in Neutral to those of the vehicle in Drive and Reverse. If the engine speed 1 lateral amplitude of the vehicle in Drive or Reverse is three times greater than that of the vehicle in Neutral, replace the vehicle’s transmission torque converter.
If the engine speed 1 (E1) lateral amplitude of the vehicle in Drive or Reverse is less than three times greater than that of the vehicle in Neutral, continue diagnosis referring to Service Information.
Parts Information
| LCV | 24265770 No products found. | CONVERTER ASM-TORQ (240 MM) |
| LTG | 24265771 No products found. | CONVERTER, TORQ |
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Last update on 2026-05-27 / Affiliate links / Images from Amazon Product Advertising API
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