Alright, My tires were wearing a bit uneven, so I decided to get my car aligned. Afterwards, the steering was loose, and the wheel would stick to one side when turning.
They replaced the axle(2yrs old), bushing, steering column, and I've done a ball joint. Still did it.

I brought it back, and they "tightened stuff", so now the wheel stays straight, but whenever I step on the gas, it jerks hard to the left, and let off, it jerks hard to the right!

Anyone know what could not be causing that?

 

I dunno, sounds serious and the place sound hokey. Worn CA bushings? Tie rods?

 

Go someplace where car is lifted and inspected while u watch: they can show you the loose bushings before you ok them to change them. My guess is pass side bushings that Jeff mentioned... (Cannot $ee why steering colum was swapped.)

Anyways your tire angles change because excess play. (Bad bearing may cause pulling). You just might feel play if u lift the tire first and grasp it with all u can.

 

same problem with me got my tire alignment and it be ok but some times jerk me to one side or the other

 

This is caused by worn out lower control arm bushings. Check the site below to see what I am talking about. The control arm has two bushings, one in the front and one at the rear. The rear bushing is likely the problem. It becomes loose and the control arm moves sideway, thus creating the feeling that someone else is driving the car.
There are two front lower control arms per car. one on each side, so get bushings for both sides. My car was taken to shop last week for an alignment. Wheels were alligned but response/handling was exactly what you described.
Some repair shop will try to sell you the complete Lower control Arm as the bushings seems hard to find, at least here in Canada. Mechanic at the shop said front bushings are likely good. In Canada I was able to get the OEM bushings for the back part of the Control arm, but not for the Front part from Nissan dealer. Check the site below. It has a good diagram and they also sell both bushings, front an rear of the control arm.



http://www.courtesyparts.com/secondtier_j30.html