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2005 Chevrolet Optra P2279 P0507 P0300 Troubleshooting: Hesitation, Misfires, High Fuel Consumption

Model: 2005 chevrolet optra Fault Code: P0300 Posted: 2011-02-21 16:03

I'm experiencing multiple trouble codes (P2279, P0507, and P0300) on my 2005 Chevrolet Optra. The vehicle hesitates and stumbles during acceleration, and fuel consumption has increased significantly. I've already checked for vacuum leaks but haven't found any obvious sources. Could these codes be related to intake air system issues or misfires? Any guidance on diagnosing and fixing this would be greatly appreciated.

Related fault codes
P0300P0507P2279
Comments (9)
Anonymous 2011-02-22 08:02

P2279 indicates an intake air system leak, P0507 points to a high idle control system RPM, and P0300 shows random/multiple cylinder misfires. Vacuum or unmetered air leaks are likely contributing factors. Start by inspecting all vacuum hoses and connections for cracks or disconnections. A proper leak test using a smoke machine or pressure test can help confirm the source.

Anonymous 2011-02-23 21:09

Thank you! I'll go through the vacuum system carefully and perform a leak check. I'll update here once I have more results.

Anonymous 2011-02-24 20:36

I found a missing vacuum cap and replaced it. The roughness during acceleration improved, but misfires still occur. Additionally, when coming to a stop, the idle drops extremely low—almost like the engine is about to stall. This may be related to the idle control system or intake airflow.

Anonymous 2011-03-22 20:24

Is this referring to the AC compressor or the cooling fan? If it's the heater blower fan, check whether the control is set to 'defrost' or 'A/C'. Also, confirm if the engine is still misfiring and what codes are currently stored. Was a recent tune-up performed?

Anonymous 2011-03-23 05:58

Thanks for the clarification! The vehicle is still experiencing misfires, and I've not seen any new codes since the last reset. The last tune-up was over two years ago—could that be contributing to the issue?

Anonymous 2013-08-30 12:30

Hi, I'm having the same P2279 code on my 2009 Chevrolet Optra. Any tips for fixing this? Is it a common issue with older Optras?

Anonymous 2013-08-30 13:16

Normally I'd split the topic, but both of you are discussing the P2279 code on an Optra—great to see! Welcome, Eduardo915. Mohawkmtrs' second post offers a solid diagnosis: intake air leaks can cause this issue. Please share your findings after checking for vacuum leaks or other sources.

Anonymous 2013-08-31 00:51

I've thoroughly inspected all vacuum lines and found no visible leaks. The car still hesitates during acceleration—only responds when the throttle is applied slowly. This suggests a deeper issue, possibly related to intake airflow or engine management system calibration.

Anonymous 2013-10-24 03:43

I finally resolved the P2279 code by replacing the EGR gasket on the cylinder head. The leak was causing un-metered air intake—when I placed my finger under the gasket, I could hear a noticeable airflow change. This is a known issue in older Optra models; parts suppliers often carry replacement gaskets for this common repair.