This is the engine in my scion, atleast I think i have the model # right.k Anyways, I've run some 5w30 and 10w30 oils in it while trying to see if anything would help quiet down my valvetrain and piston slap noises. This car of course calls for 5w20 or 0w20. I've noticed when running the thicker oils, especially my last oci using Castrol Syn. Blend 5w-30, it seems a little more sluggish, particularly in the lower rpms and I can feel "steps" in the power band, similar to the older honda engines with v-tec where they would switch to the higher lift/duration lobes on the cam. At first i thought it might just be my injectors starting to get dirty as I havn't run any fuel system cleaner through it in the past 15,000miles and had always done that once every oci in the past. I am currently running Mobil Super 5000 5w20 in it and have noticed bottom end when pulling out from a stop seems a little better, and the power band seems smoother. My theory is the thicker oil was affecting the opertion of the cam phazers and this is why I felt the differences in the power band. Do you guys think this holds any merit?