Reader Question I have a 1997 Ford Expedition and we replaced all 4 of the O2 sensors this spring (one at a time) and now they are all bad again. What can cause them to go bad? My engine is “boggy” when in the idle position, especially when air conditioner is on. Should I address this immediately?
What do you mean by “boggy” that’s a new one on me. If the idle is rough (not nice and smooth) or the idle speed surges or fluctuates I would suspect you have a dirty throttle body and or dirty idle speed control motor, or a faulty idle speed control motor.
Changing all the o2 sensors is uncommon, doing it twice….either you have a misdiagnosis or something weird is up. The only thing I can really think of that would cause damage to the o2 sensors would be using some kind of fuel additives or a restriction in the exhaust system like a stopped up catalytic converter.
I am assuming the check engine light is coming on…which it should if you have bad o2 sensors, but the light might not come on if you have a dirty idle motor or throttle body.
How well do you trust your mechanic and his expensive diagnosis? Should you get a second opinion….I probably would.
Faulty o2 sensors can cause the check engine light to come on, poor fuel mileage and poor engine performance – lack of power, and probably cause you to fail an emissions test.
Austin C. Davis
Reader Follow Up
Yes, the check engine light is on and the engine is just as you described it during idle. Surge and fluctuate. I am a single person and worry about getting taken advantage of.. First person I talked to said it was probably catalytic convertercausing them to go bad like that. Hmmm… We’ll see.. how much can you save in fuel mileage? Is this something I should address right away? Thank You for your response.
Hello again Natalie
I would get a second opinion first before we can really determine the seriousness of the situation. Find a quality repair shop in your area that is capable of reading the onboard computer codes and diagnosing the problem.
You are probably ok to continue to drive like this for awhile. The fuel mileage could be hampered by as much as 50% IF the o2 sensors where really bad.
Let me know what you find out.
Austin C. Davis