I have an EG4 with a D16Z6 engine, but when I'm driving fast, it becomes very unstable. I recently discovered that the front subframe was in very bad shape. After replacing it, the car remains unstable. I don't have any worn bushings or anything like that. What should I do to improve handling?

 

Have you had it align?

 

Yes, I had the alignment done. Could worn-out suspension springs be causing this? :/

 

Is the car lowered? Are the struts good? Any body/sub frame rot/rust?

Tell us more about what the car does at that speed that makes it unstable, does it get bouncy, goes left/right, does it have too much play in the steering wheel....

 

The car is at its normal height, the shock absorbers are new KYB. It lifts and pulls to the right, a slight play in the steering wheel is noticeable, and the steering becomes quite sensitive at that speed.
When I'm at that speed or higher, the steering wheel feels very light, practically loose in my hand.
The car has already been in a frontal collision, and so far what I've indicated is that the bolts holding the front assembly are bad; some kind of shoddy work was done.
Something silly, but strange, when turning onto a street the steering wheel doesn't return to its original position, I have to do it manually.
Thank you for your patience and help.

 

Sounds like the rack and pinion is toast or you have ball joints that are binding which requires replacement

 

Or the alignment is junk. Do another alignment. Make them print off the results. Make them check caster and camber. Neither of those are factory adjustable but bad caster or camber will be a clear sign something is bent. My guess is caster related. Upper or lower arm is skewed. Steering not returning to center with light steering feel sounds like bad caster and not something like a binding rack.

You also might have play in the steering column. Small issues in multiple components compound issues. Its important to brace each section of the steering and test each link/section for play/slop.

 

Thank you very much for your help, I will check those points.