Fuel System - Cold Start Idle Fluctuation Explanation
NUMBER: 11-84-07DATE: 10/15/07
APPLICABILITY:
2005 and Later Naturally Aspirated
(Non-Turbo) PZEV (Partial Zero Emission) models
SUBJECT:
PZEV Idle Fluctuation after Cold Start
INTRODUCTION
This bulletin is for informational purposes only.
If you encounter a customer complaint about an idle fluctuation ("hunting") during cold starts which generally last about 20 to 30 seconds the cause is a combination of factors.
Some of these are:
^ Fuel blends
^ Percentage of Ethanol content of the fuel being used
^ Temperature
^ Narrow operating range of the Air Fuel Ratio Sensor The main cause of this idle fluctuation is fuel related and not the vehicle.
PZEV engines are designed to run on fuel blended for distribution within certain areas of the U.S. (such as the state of California). Fuels available in other markets, that may have adopted California emission standards, may be a slightly different blend. If you live in any other state than California, your vehicle will operate on gasoline meeting Federal specifications. However, PZLV vehicles may experience this issue especially during the summer months when summer blend fuels are distributed. 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 or no Ethanol Also, a light throttle application while the vehicle is exhibiting this condition will stabilize the idle. As we move towards cooler weather many areas of the country will be changing to a winter blend of fuel which may also alleviate the condition
If this condition is confirmed, no repair attempts should be performed beyond confirmation and checking all other systems are operating within design parameters.
Disclaimer