Look at the Idle Air Control first. Also, make sure the air filter is clean; if it's really loaded, you won't get enough air to run with a closed throttle. Check the throttle body idle air intake passage(s) to make sure they are clear.
SOURCE: HAVE A TROUBLESHOOTING MESSAGE PO446
DTC P0446 Evaporative Emission (EVAP) Vent System Performance
The vehicle control module (VCM) monitors the performance of the evaporative
emission (EVAP) system by applying a predetermined level of vacuum to the
EVAP system and monitors the vacuum decay rate. The VCM sets this diagnostic
trouble code (DTC) if the vacuum decay rate is more than a predetermined
value. The VCM monitors the amount of vacuum and the amount of pressure
in the EVAP system by monitoring the fuel tank pressure sensor. For
this DTC, the VCM turns ON both the EVAP purge valve and the EVAP vent
valve when the Conditions for Running the DTC are met. This applies
an engine vacuum to a closed EVAP system. The VCM turns OFF both the
EVAP purge valve and the EVAP vent valve when the system reaches a correct
amount of vacuum. The EVAP system should quickly RELEASE the vacuum
in the EVAP system with the EVAP purge valve OFF and the EVAP vent valve
OFF (open). This test indicates a blocked or restricted EVAP vent path
if the EVAP system fails to release the vacuum quickly enough.
SOURCE: 2003 Camry won't stay idling after I changed battery
This is extremely common :)
With time your throttle body gets gummed up with oily residue from the PCV system. As this happens, the computer adapts to the restriction it causes in the throttle body.
When you unhook the battery, these learned values are lost and the default settings for idle control are used. Unfortunately the default settings are no longer sufficient to keep the idle correct with it all gummed up.
Take your intake hoses off the throttle bodies and clean the insides (open the throttle plates for better access) with a rag and some brake parts cleaner or throttle plate cleaner, available from your local parts store.
Reassemble and start the car, your idle problems should be gone immediately.
I
SOURCE: My daughter's 2003 Mazda Tribute sometimes won't
Go to my profile and see my tips for how to fix this. You can fix this problem quickly and easily without buying a new idle control valve...just clean and lube the existing valve, it's very simple.
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