Question about 2000 Toyota 4Runner
Change your oxygen sensors - they're responsible for feedback that the computer uses to determine the air/fuel mixture. They usually are good for about 60k miles and then start to go downhill. When they get to a point that the computer won't trust them, it ignores them and runs on preprogrammed fuel maps that run excessively rich (too much fuel) to safeguard the engine. You've probably seen a decrease in fuel mileage as well. And the O2 sensors have to be up around 900 degrees before they'll work - the car ignores them until then. That's why you run fine after a cold start but run rough once the car is warmed up.
The O2 sensors you want to change are in the exhaust system between the engine and catalytic converters (the "pre-cat" sensors). There are O2 sensors after the cats as well, but those are used comparatively to determine how well the cats are functioning. The primaries are the ones used for fuel mixture. If it's been this way for a few weeks or so, I'd put new spark plugs in as well - rich fuel conditions can foul them and contribute to the rough running.
Posted on Dec 09, 2009
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Posted on Jan 02, 2017
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