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2003 Mazda Protege P0300, P0400, P0113, P0103, P0102 - Idle Issues and Misfire Diagnosis

Model: 2003 Mazda Protege Fault Code: P0103 Posted: 2007-09-13 21:39

I own a 2003 Mazda Protege LX with a 2.0-liter engine and am experiencing recurring idle problems. The car runs fine under normal conditions but begins to struggle when idling—typically at around 200 RPM, where it sounds like it's nearly dying but remains running. Notably, the check engine light does not illuminate during this condition. I recently replaced the spark plugs with a gap of exactly 0.75 mm (as per manufacturer recommendations), but there was no improvement in idle stability or performance. When I had a friend disconnect the Mass Airflow (MAP) sensor, the check engine light activated immediately. A second friend connected an OBD-II scanner and retrieved five diagnostic codes: P0102, P0103, P0113 (likely related to MAP sensor disconnection), P0401, and P0300—where P0300 indicates a general engine misfire. The vehicle has 82,000 miles on the odometer. Possible causes I'm considering include faulty fuel injectors, ignition coil issues, or oxygen (O2) sensor failure. However, given that the MAP sensor disconnection triggered the check engine light and multiple codes, I suspect a deeper issue with airflow or fuel delivery. Any insights into diagnosing these specific codes on this model? Is there a known common fault in 2003 Mazda Protege engines related to idle instability or misfires?

Related fault codes
P0103P0113P0300P0401
Comments (4)
Anonymous 2007-09-14 07:13

The EGR system is likely the root cause—this is a very common issue on older Mazdas, especially around 80,000 miles. A clogged or stuck EGR valve can lead to poor idle and misfires due to incorrect air-fuel mixture.

Anonymous 2007-09-26 17:18

I have a 2001 Mazda Protege ES 300 (4-cylinder) with 80,500 miles and am experiencing the exact same symptoms—P0300 code today. I also hear a noticeable shaking sound when driving in D gear at low speeds or standing still, which sounds like two metal parts vibrating against each other. Any advice or troubleshooting tips would be greatly appreciated.

Anonymous 2007-09-28 08:41

Have you tried any diagnostic steps yet? For example, checking the EGR valve, inspecting the PCV system, or testing for vacuum leaks?

Anonymous 2012-01-12 08:56

This is an older post, but I believe the spark plug gap of 0.75 mm may be too small. I typically set my plugs to 0.045 inches (just over 1 mm), which has proven more reliable on my 2003 Mazda Protege. I've noticed consistent misfires—often due to excessive oil being sucked through the PCV valve, a known and widespread issue in this engine model.