Subaru idle jitters
This TSB applies to all 2005 and later Subaru Outback non-turbo PZEV (Partial Zero Emissions) models. Customers may comment about an idle fluctuation (hunting) during cold starts, which generally last about 20 to 30 seconds.
The causes have been attributed to fuel blends, ambient temperature, percentage of Ethanol in the fuel and the narrow operating range of the air-fuel ratio sensor.
According to Subaru, the main cause of the condition has been fuel-related, not vehicle-related. PZEV engines are designed to run on fuel blended for distribution within certain areas of the U.S. (such as California). Fuels available in other markets, that may have adopted California emissions standards, may feature a slightly different blend. If the vehicle is operated in any other state than California, the vehicle will operate on gasoline meeting federal specifications. However, PZEV vehicles may experience a hunting-idle issue especially during the summer months when summer blend fuels are distributed. According to Subaru, there is no effect on vehicle emissions, and no short or long term damage will occur due to this issue.
The condition may be reduced or eliminated by changing to a fuel that contains a lesser percentage of Ethanol. Also, a light throttle application while the vehicle is exhibiting this condition will stabilize the idle. In winter months, distributors will change to a winter blend of fuel which may also alleviate the condition.
If the cold-start idle-hunting condition is confirmed, no repair attempts should be made beyond confirmation and checking that all other systems are operating correctly.