Reading codes PO340 and PO300

98 sidekick automatic 4x4 idle surges up and down when cold and levels off to a stall out after warm and runs rough and can not drive or it wont go fast enough.I replaced o2 sensors as it needed them for a good while, than the maf and after that a few days it started rough idle, my cat was not even a year old. Now I hear a rattle sound in it like something is bounceing around in it. When I rev the motor it revs good just wont idle right and in drive has no pick up just boggs. Thanks for any help you can spare. Mj