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What causes -30% long term fuel trim


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-30% long term fuel trim, close to 0% short term fuel trim on an 05 tundra 4.7. Recently purchased. It appears to get fairly regular mpg. What are possible causes? 217k miles and 2wd. 

Since Recently purchased I have replaced spark plugs, air filter (oem has more pleats! And similarly priced), pcv valve (just one?), and will do the timing kit soon. All oem (or aisin) parts


I would like to think I'll keep it until around 500k miles

This topic was modified 6 days ago by Chadlord23
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2 Answers

Do you have codes? You should. 30% rich is pretty extreme. Lots of stuff can cause a rich running engine.

Check your air filter, if it's dark when you hold it up to the sun, replace it.

Do Scotty's video, how to make your car run better with spray cleaner and do what he does.

Run fuel injector cleaner. Dirty injectors can cause fuel to drip instead of atomize like it should. 


Clean the MAF sensor and throttle body.