It has no take off power and bogs down bad goin up a hill
First thing I think of when this problem occurs is your catalytic converter is plugged. Too much back pressure in your exhaust system will cause this exact problem. Do you notice any odor when this bogging occurs? A simple test would be to disconnect the exhaust before it enters the cat. It's going to be loud as heck, but if your power returns, you found your problem. Replace the CAT.
Search Hyundai Elantra Questions
Hyundai Elantra Experts