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My wife's car is a 2007 4cyl 2.4L Toyota Camry with 160,000 miles. Very well maintained, no drivability issues, no check engine light. Total fuel trim at idle was a little high yesterday at around positive 18 when my wife got home from work. The day prior, the car only made one short local trip and total fuel trim was around positive 13ish. Total fuel trim driving, accelerating is around positive 6. This car has had slightly high fuel trim for years, but in the past was around total of 12 or 13 positive. This new positive 18ish range is causing me some concern. 02's show full rich at WOT, so I'm not suspecting a fuel delivery issue. I've smoke tested the engine, and aimed propane around the intake area and can't find any evidence of a vac leak. Frustrated at my inability to track down the high fuel trim at idle, I replaced the intake manifold gasket thinking maybe there was leak so small I couldn't detect it. No change. I'm wondering if perhaps my valve lash could be a suspect here. Not all the time... but sometimes I think I hear some rattling, perhaps from the bucket lifters. So... two questions. (one) any other ideas of what could be causing my high fuel trim? (two), if it was the valve gap between some of the lifters being out of spec, would that cause high fuel trim ONLY at idle? Or if valve gap was out of spec, would that show a fuel trim problem IN ALL CONDITIONS (idling and under load)?
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