Hyundai Repair: 03 2.7 v6 tibron shaking, throttle position sensor, auto parts chains

Question
I have 03 tibron 2.7 automatic v6 .The engine shakes when it
just sitting there and when you drive. I replace the MAF but
that was not the problem. has new spark plugs and wires.
When i turn the battery off for aa long time it seems the
car resets and the problem goes away. but once i go to drive
it the problem comes back. Now for the problem.The rpms will
go anywhere for 1/2 to 3 it changes all the time. The engine
shakes. The car will sometimes start to work great then it
kicks back into bad again instantly. there is a misfire in 3
of the 6 cylinders on the codes. Struggles to get going most
the time and wont change gears till like 6 rpms  some times.
no idea what to fix. or whats wrong.  

Answer
Hi, Robert.  With all that is occurring, I'd expect that your check engine lamp should be on and some diagnostic trouble codes should be stored.  If you can read the codes-- most auto parts chains will do this for free-- and report the code numbers back here, it'll help me understand what is occurring.  As it stands, it'll be helpful to know what type of shaking the engine is doing: whether it's a misfire or simply a varying idle.  I understand if you're not able to give me that much detail regarding the shaking.  In such a case, the trouble codes will likely be able to give me significant information regarding the nature of your problem.

Since you've already changed the plugs and wires, consider that if the car is misfiring, it could be for other reasons as well:
-- faulty ignition coil
-- low compression
-- clogged fuel injector.

Also, the fact that you mention a changing idle leads me to believe that you may have a large vacuum leak somewhere or that the throttle position sensor may be defective.