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OnlineHelp, Mechanic
Category: Car
Satisfied Customers: 3423
Experience:  Mechanic
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Mazda MPV: check engine light..the highway..hill..stop sign

Customer Question

My mazda MPV 2004 has a check engine light on. During acceleration and while on the highway (especially on a hill), the car chuggs and bucks fairly often; sometimes it accelerates fine. Sometimes, but not nearly as much during acceleration, it will chug while stopped at a stop sign. Can you please tell me what might be causing this?
Submitted: 6 years ago.
Category: Car
Expert:  OnlineHelp replied 6 years ago.

Hello and thank you for choosing Just Answer.


This is a air/fuel ratio issue. Either the Mass Air Flow is not regiestering the amount of air correctly or the fuel supply is low. (Bad pump or bad fuel pressure regulator).


Since the check engine light is on, the car has already found a fault in the system and stored it as a code. I would suggest that you have the car scanned to find out what the car has found.

This scan typically costs about $90 at most shops. However if you take the car to parts stores, they will do the scan free. Simply ask for an OBDII scan and print out. This will tell you what needs to be reparied/replaced.



Customer: replied 6 years ago.
OK, I went to Autozone and got a reading. The code was P0303 (Cylinder misfire condition detected) Probable cause: Lean Air/fuel ratio; Weak ignition system; Engine mechanical condition; vacuum leak affection one cylinder. Not sure what to do now....
Expert:  OnlineHelp replied 6 years ago.

Thank you.


P0303 means that cylinder #3 is misfiring. Most likely a bad spark plug, ignition coil, or fuel injector.


In the back of the car right side.

2004 Mazda MPV
3.0 liter DOHC V-6


I would start by checking the coil. Remove the coil from cylinder #3 and switch it with coil #5. Then disconnect the battery and wait for the check engine light to come on. When it comes on have it scanned again. If the codes is now P0305 that means cylinder #5 is misfiring. (Bad ignition coil). If the code remains switch the spark plug. See if the code changes. If the codes is P0305, you have a bad spark plug.


Finally if it's not the spark plugs or coil (which I assume it will be ) you will need to switch the fuel injector and see if the code changes.



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