Honestly, ts's username quite obscene lol..

oir at least that is the preferred name by this member.Yup, probably need another shop or mechanic to check if anything is loose.....Makes me doubt the quality of alignment work there as well.
Before I did my balancing and alignment, I noticed at times the steering shaking lightly and I let go of my hands from the steering wheel, it would slowly swerved towards the left side.
That was the reason I sent my car for wheel balancing and alignment. And now I found out this new problem. The swerving movement is as if my car being lifted up by strong gust of wind or speeding thru' a big patch of water on the road.
Go get a 2nd opinion and redo alignment.
Initially I thought it was torque steer until I saw what car you drove then that thought went out the window. Unless you have a 4G63T inside?
And what RPM do you experience this swerving? Do you feel it even when driving slow or only when you accelerate hard?
Possible that your car undercarriage/sub-frame is very loose/flexing alot. I mean since you say is an old car.
