Steering wheel not centered

This might be the first time since you owned it that it is actually working right.

IF.....the deviation really is slight, it might just be compensating for the crown in the road and you actually are steering a tiny bit to the left to keep from "running down the hill" and off the road.

This would explain why it is different sometimes than others.......because some roads have more crown than others.

NOTE: A road "crown" is when the center of the road is higher than the sides......so that water can run off better.

 

Centering the steering wheel is one of the primary objectives of the wheel-alignment procedure. If the steering wheel is not centered, you need to take the car back to the shop for realignment free of charge.

Correct procedure is such that the technician sets the steering wheel exactly in the center, locks it in place with an anchor to the brake pedal so that it doesn't move during the wheel alignment, and then adjusts the front toe-in by adjusting the lengths of the left and right outer tie rods. The left and right toe-ins are usually set to 0° both. If not, they need to be exactly the opposite angle for the car to go straight with the steering wheel in the center.

There is another cause for an off-centered steering wheel, but this is rare. Nevertheless, it did happen in my previous car. The toe-in could be correct but the steering wheel itself may have been mounted asymmetrically on the steering shaft's grooves. You can easily check if this is the case. Set the steering wheel so that the front wheels point exactly to the front. Then count the number of turns to the left lock and to the right lock. The number of turns to the left and right locks need to be equal. If they are different, wheel alignment cannot be correctly performed until the steering wheel is removed using a steering-wheel puller and it is repositioned on a different groove of the steering shaft so that the number of turns to the left and right locks are identical. After this is done, front toe-in is readjusted. Once again it is impossible for the front toe-in to be proper unless the number of turns to the left and right locks are identical. However, shops usually never check for this and will send you home with asymmetrical outer-tie-rod lengths (because the toe-in is set for a turned steering wheel without realizing it), assuming that this is the way it is for your car.

 

If the 'centered' position actually moves around more than a tiny bit, there is probably play in some front end component like a ball joint or bushing, allowing the alignment to shift around under forces from the road.

About a year and a half ago I was visiting a relative and had to drive her car for some errand, and noticed 'straight ahead' could shift around by 90° on the steering wheel depending on whether the most recent turn was a right or a left! She had just been driving it that way.

I had some words with her about how I might just put up with it if 'straight' were always consistently a bit off, but moving around like Igor's hump was not a thing to ignore, and after I left she took it in and there were several bushings, a ball joint, and a wheel bearing replaced, and then 'straight' didn't shift around any more.