2001 Kia Optima Vibration.I took it to the shop, they replace the timing belt and balancer shaft belt and components and it still vibrates. What is the cause ? The vibration is so severe it rattles the car body.

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Could be wheel bearing or wheels need balancing or a warped brake disc

I had 2006 kia optima 2.4 liter LX, I drove 150000 miles plus, it was over 100,000 miles I changed timing belt, and AC belt, alternator belt is still ok, but it was my fault, I did not change crank shaft balance belt, it next to timing belt, this very important, timing belt and crank shaft balance belt must change same time, you set all mark the same positions, you can see all clear marked
if you had OBD2 scanner is helpful to read all faulty codes if you do it your self repair
if you have any problems about KIA optima, please post on any websites, to share some ideas to other KIA optima owners, like me, I change oil every 2500 miles to make my optima runs smoother
automatic transmission fluid change every year if you put high mileage on your car, optima had hard time to find it own part some time, radiator hoses are still good condition and had hard time to find in any auto part stores in my home town, good luck and thanks for sharing.

I have been dealing with the same issue in my 05 kia optima for over a year with the vibration getting worse as time went on. I found excessive carbon buildup on the counter balancer shaft which put the shaft out of balance. The vibration started out very light in the beginning and continued to get worse as time past to the point that the steering wheel would shake in any gear that the car was in. We found this solution almost by accident by turning the balancer shaft by hand an felt a very slight roughness while turning it. That is when I made the choice to pull the shaft out an we send a very visible problem.

Did you put alot of pressure on belt when installed ? to tight will cause that vibration

is your vibration at 43 and 54mph coasting or under acceleration?
we had a car in the chry shop once with sort of the same problem,i brought another identical car in a different bay,removed all four wheels from our car to customers,road tested customers car afterwards,still had the vibration,brought it back in a took the time to swap cv shafts,road tested again,but still had the vibration.it ended up being the bushings in the transmission that keeps the CV shafts from wobbling.

It sounds as though the timing may be off. The belt may be okay, but if the timing is off, it will cause the motor to vibrate. Also... if your car keeps chewing up timing belts, there may be a defect in the timing gears or belt guides causing the belts to fail. There is also the possibility that the timing belt is rubbing against the timing cover as well. If the car seems slow to accelerate, or just doesn't perform as it once did, and it vibrates at idle and when you accelerate, there is most likely a timing issue still, and you need to ask your mechanic what they can do to remedy a problem. I hate to say it, but there ARE bad mechanics out there, and although I do not know the one that you used, many techs that put a timing belt in a car and find out that they are off a tooth on the gear will not tear it back apart to redo it. It is a lot of work and they are getting paid once to basically do the job twice. They'll give it back to you and just hope you don't notice. I can't promise this is the case, but its food for thought. Wish you the best in getting the timing issue resolved!

sounds like you got it a tooth or two out of time

There are Two Balance Shafts on the 2.4. Did your mechanic also change the balance shaft belt when he changed the timing belt? If he didn't, you'll want to do that. Since you mentioned the old belt was missing teeth, those loose teeth flying around could have damaged the crank position sensor and sensor blade (tone wheel). Also, the front balance shaft (on the side of the engine nearest the radiator), has THREE different positions when the timing mark is lined up - here's the glitch - ONLY ONE of them is the correct one - this is probably where your vibration is.

you have to change the shaft also