I have a 2000 Toyota Avalon. It started misfiring last week, this is like the 3rd time this year. They just swap the spark plugs and it seems to work fine for a couple months then BAM! Misfire. I’m stumped:
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I am guessing here because so much information is lacking…
I assume this car has loads of miles… 150K plus… Right?
I will guess it uses a quart of oil every 2000 miles, or maybe 1500 miles, or even 1000 miles. Which is it?
If the engine is burning oil, that can foul the spark plugs and cause a misfire that can be cured with new plugs… The car uses more oil, fouling occurs, new plugs. If the same cylinder misfires every time, that one cylinder’s rings may be worn out so oil consumption won’t be super high.
If an injector is getting stuck and dumping extra fuel into one cylinder, that cylinder can misfire when the plug fouls from excess fuel. A check engine code for “rich mixture” should be set as well as the misfire code.
Have a compression test (wet and dry) on the engine. If that shows OK, you might assume it is the injector or injectors.
A good mechanic would have already done these tests (but not for free…) or at least suggested them. If yours did not, find a better mechanic!
There is a lot more to misfire than swapping plugs. The root cause is something else. Find another shop.