Rear hub nut on a2003 hyundai elantra

Question edited for clarity.

Possibly, some do cover things that affect starting, the 'fuel pump relay' for instance. You need to diagnose, not just replace as a guess. Check for codes. A prograde scan tool will diagnose all modules and relays.

https://www.autogenius.info/hyundai-elantra-2005-fuse-box-diagram/

..

Look for a hose coming out of your firewall running down to the bottom of the car

"BING SEARCH" http://www.bing.com/search?FORM=UP97DF&PC=UP97&q=How+to+remove+the+rear+bumper+cover+on+2013+Hyundai+Elantra

remove the interior door trim and you will see small nuts holding the handle onto the outer door skin. Remove any rods /clips and undo the nuts and the handle will come out.

WHERE IS AIR CHARGE TEMP. SENSOR LOCATED ON A 2003 HYUNDAI ELANTRA

Hello,
are you talking about the wheel lug nuts ? if you are they would be 65 to 80 lbs.
good luck

it can if you have the proper tools and a little patience its not very hard at all it may be a little snug i cant remember off hand where the starter is located on that car but its relatively an easy fix.

With the car on ground, break loose the drive-axle nut, and the wheel nuts , than jack up the car, support it properly, remove the wheel ,remove the axle-nut.
Remove the brake caliper assembly-- support it properly.
Remove the two bolts that hold the hub bracket to the Macpherson strut assemble, remove the lower arm ball joint and remove the steering tie- rod ball-joint attached to the hub bracket. That's it.Slide off the hub /with the bracket off the drive-shaft.
Follow steps backwards to assemble back.

Did you use a aftermarket O2 sensor or a genuine Hyundai one? If it's an aftermarket one it may be bad or not as good as the OEM one. See here for more details and other potential causes: P0133

grab a large punch and hammer and knock out the old broken one. Push the new one in and re tighten. This will pull it into place and because it has splines it should not spin while doing so.