My 01 4runner has a problem with dropping rpms to the point of almost stalling for a second while shifting into reverse and more so while shifting into drive. Doesn't matter if hot or cold or if the AC is running. I've cleaned the MAF sensor and the TB, replaced the air and fuel filter, checked the plugs and alternator, and the engine isn't throwing any codes. I have a scangauge II and notice the air to fuel ratio drop from about 14.6 to 12 when this is occurring. The engine has unknown mileage, I'm guessing around 260,000. It also runs rough while idling in second gear like if I'm coasting through a turn or driving in a parking lot. I punch the gas and it chugs for a bit then snaps out of it. I'm running out of ideas...