[jyukumite]

For anyone else who finds this thread like I did:

2013 86 GTS. New and unsettling understeer mainly on long left sweepers, it seems to jump between two lines, corners like something is loose. On a long left sweeper at ~90kph when the TC light started flashing, it got real*.

Pulling and pushing on the front wheels, really can't feel anything wrong on the pavement. Nothing feels loose when stationary. No codes, doesn't seem like TC/wheel sensors. Mechanic told me the tires were shagged and to lay off the aggressive driving, said there was nothing wrong (I called BS). Tires were over it (18mo and at the indicators), but I switched front to back with no real change. Changed out for four new tires anyway, alignment was about what it was when I got the setup. Problem still there...

Got it home, put it up on jack stands, found that swinging on the front RHS rotor with the suspension unloaded and at full lock is enough to see a tiny amount of slop in the lower ball (not the LHS though).

Aaron Klaver/Import Monster: Have seen it a few times where the castle nut on the ball joint has been tightened with the ball joint not seated properly. Under load it was riding up and the steering geometry was changing mid corner. Straighten up and it plonks back into place. You could feel the toe change mid corner.

Well, I got nearly a whole turn out of the RHS ball nut before it gave any resistance at all. LHS was close to the correct torque already. It tracks properly around corners again! Turns out cars go better when a wheel isn't LOOSE.

Thanks Aaron!

*oversteer scares passengers...understeer scares the driver