Here is your $0.99 diagnostic. (And welcome to my world.)

Get a can of carb. cleaner and while the engine is running, spray it along the intake manifold mating surface. If the engine speed changes then you've found a leak.

One other thing to check that I've had a problem with on mine, are dragging brakes. Go for a normal drive for 10-20 min. Then get out and feel the heat coming off of each rotor through the wheel spokes. If you had a brake caliper that isn't releasing properly, there'll be noticably more heat coming off of that rotor. (For more precision, use a digital, non-contact, infared thermometer.)

Good luck!