i thought i had a vct solenoid problem. the car would jerk and hesitate when starting out and just after shifting gears and attempting to accelerate. i replaced the coil, but it felt like a timing problem. the problem started just after an oil change where i ran 10W-40 instead of the usual 5W-30. i read on the internet somewhere that the vct is pretty fickle about the types of oil it can effectively use, so i changed back to 5W-30 and that fixed the problem. i know it sounds crazy, but the vct uses oil pressure to retard the exhaust camshaft and if the oil isn't the designed viscosity, then it seems to not work too well. i would try changing the oil to 5w-30 before any major work.