I have a 2002 996TT with 27K miles, stock OEM tires and wheel with a set of JIC Cross coilovers installed. I have been messing with this for 2 years now and cannot seem to get it figured out.
Currently car is set to GT2 ride height with X73 alignment done most recently at Porsche. I am attaching the alignment print out.
The issue is at speed, above 80) the car wants to hunt right an left like it following grooves in the pavement and at say 120 it is downright scary to keep it pointed straight.
Checked with JIC and they don't see anything wrong with the way the car is set up. Sent this to RSS and waiting to see what they might think as well. Porsche wants to put some adjustable thrust bushings in to correct the castor but not sure that is much of an issue or worth $1500 just to try it out.
Any of you guys been through this that could shine any light on what might be a solution?
Thanks alot for your help.

 

Worn out control arm bushings or tie rods will cause that. The best way to check is to Jack the car up. Make sure the steering wheel is locked. Rock the front wheels in all directions and listen and feel for clucks. If it clunks, take the wheels off and to see what is worn out. I am betting on a worn out ball joint on either the lower control arms or tie rods. The other thing I would check for is losened hardware. Good luck.

 

I have the same wondering problem with my 2004 Tahoe. I jacked it up looking for play in the front end and got nothing. I took it to my honda mechanic and he checked with pry bar. Told me tie rod ends are bad both sides. Make sure you check with some force and leverage similar to what the car would see in the real world.
I have the H&r springs on my 03 996tt and while I have only seen 130 1 time, my car is very stable.

 

For a nice street setup I say get camber to -1.5 font and -2.0 rear with 0 toe. Inspect and replace a few suspension bits. Car is pushing 10yrs old. Changing the rear dog bones on mine made a difference. My car's tail end would dance on the highway while accelerating. Adjustable toe links will help. I also put some wheel spacers on mine; 15mm rear and 7mm front.

 

It looks like you have some toe-out in the rear. For more stability
you'd want a little toe-in all around. But I'd make sure the bushings
and rod ends are all tight first.

 

What effect on the drive do the spacers give?

 

+1 for Joe .... adding toe will help stability.

The car is lowered, you didn't mention what if any sway bars you have. Do you have adjustable sway links? I have seen cars lowered on stock sways and links. lowering the car specially if it is corner balanced can cause uneven sway bar loading and lead to weird handling.

Adjustable thrust arm bushings are a good thing. Go with solid in the rear as well

This can be a real slippery sloop. It is easy to spend 10-12k on suspension upgrades and it does make a huge difference.

I almost forgot to ask the simple question. Is the handling problem consistent on different roads? Some roads specially older two lane back roads are just bad. Tire pressure can make a big differance as well. Could also be the tires themselves.

I better stop I could go on and on ....

 

I run the spacers on my stock wheels. It gives the car a bit wider track (better stabilizes the car). Also have you done a conner balance on the car. Your weight distribution could be a bit off. What kind of shop did you take it to. Someone who knows Porsches and tracks them? That would be my recommendation.