Son's car chugging

  • 4 CYL
  • 2WD
  • 120,000 MILES
My son has a 2002 Mazda Protege 5 with about 120,000 miles. Up until this weekend, it ran like a top. All of a sudden, on Saturday morning, it started running badly. He says it chugs when idling--almost as if it's trying to run on 3 cylinders. On the highway, it runs less than adequate and is suddenly sucking gas. Yesterday afternoon he replaced the two ignition wires, the four spark plugs, and the air fileter. Still, the problem persists. I suspect a clogged fuel filter or perhaps an oxygen sensor problem. Any ideas?
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Sunday, January 9th, 2011 AT 7:59 PM

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One would think the clogged fuel filter idea wouldn't cause an increase in fuel consumption. However, anything is possible. If it is chugging, I first would recommend replacing all plug wires, not just 2. Also, check for vacuum leaks. Finally, if it feels like a miss, tell him to carefully, with the engine running, remove one spark plug wire at a time. (This is old school). Each plug wire that he removes should cause a miss in the engine. If it is a dead miss, when he removes the plug wire to the affected cylender, there should be no change in the engine performance. That way he will know what cylender to focus on (plug, wire, compression.). Also, an O2 sensor should have turned on the check engine light. If it is on, have the computer scanned for trouble codes to identify where the problem is coming from. Tell him to also pay attention to any smoke from the exhaust (white, black, blue.). That could indicate a specific problem too. Finally, please tell him to only remove one plug wire at a time and replace it for the test before moving on to the next. Also, MAKE SURE TO USE INSULATED PLIERS to remove them so he doesn't get shocked. Let me know if you have other questions.
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Sunday, January 9th, 2011 AT 11:16 PM

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