A valve characteristic controller for an engine including variable valve
actuation mechanisms, one for a first valve and another for a second
valve, to vary the opening and closing timings of the valves. The
controller executes main control to calculate a target timing of the
first valve in accordance with an operation state of the engine and has
the corresponding variable valve actuation mechanism adjust the timing of
the first valve to the target timing. Further, the controller executes
sub-control to calculate a target timing of the second valve based on a
target valve overlap amount and the actual timing of the first valve and
has the corresponding variable valve actuation mechanism adjust the valve
timing of the second valve to the target timing. The main control is
executed on the one of the two variable valve actuation mechanisms having
a lower response speed.