Mazda 3 2006 2.0L Rough Idle and Stalling with OBD-II Code EVAP Monitor (Cap Off)
I'm new to this forum and am seeking help diagnosing a recent issue on my 2006 Mazda 3 2.0L. I've noticed the vehicle has been experiencing a rough idle, especially at certain elevations. The idle is now inconsistent, and it has started to stall intermittently when idling—though not frequently. I recently used an OBD-II scanner and received the error code 'EVAP Monitor (Cap Off)'. I have no prior experience with vehicle diagnostics, so I'm unsure what this means or how it might relate to the rough idle or stalling. While there's currently no engine light on, I'm concerned about potential underlying issues. I've also considered cleaning the throttle body due to visible dirt buildup, which could be contributing to the idle problem. Could this code and symptom be related? Any insights or troubleshooting steps would be greatly appreciated.
Please share the exact OBD-II error code displayed by your scanner. Regarding the absence of an engine light: when starting the vehicle, the Check Engine Light should illuminate for approximately 3 seconds and then turn off. Confirm this behavior to ensure proper system operation. If the EVAP monitor is not yet ready (i.e., it's in a 'monitoring' state), that may explain why you're seeing the 'Cap Off' message—this typically indicates the vehicle hasn't completed its evaporation system self-test, and doesn't necessarily point to an active leak. However, it could still be related to idle stability if there are underlying sensor issues or vacuum leaks. Clean throttle body is a reasonable step, but verify that the code is not indicating a deeper issue.