Shimmy in 2003 Ion
 

I have a 2003 Saturn Ion 2 (5-speed) with 118000kms. Lately it has been starting to really shimmy at hightway speeds and I can really feel it on the steering wheel and see the wheel shake if I take my hands off. There is a slight knocking coming from somewhere inside the front of the car. This has been tough to diagnose because it only does it about 50% of the time, and seems to stop when I am turning. Does anybody have any clues?

90% of the time a shimmy in the steering wheel is caused by tires/wheels that need to be balanced.

The first thing to check as to the knocking noise would be the front swaybar bushings.

I have already replaced the sway bar bushings a few months ago. While this knock is similar, it is not quite the same.

I guess you did not inform us when you made your post that swaybar bushings had been replaced, still I'd check them.

Check the boots on your CVCC joints - make sure they are not torn/ripped/missing. Jack the front, and check for excessive play/slop in the CVCC joints ......

How do you check the sway bar bushings without just replacing them? When I replaced the other ones, they didn't even look worn.

As for the shimmy, if something was out of balance, why would it only do it half the time? I agree though, that is exactly what it feels like.

Shake Rattle and Roll
 

Take it to an alignment shop. A good one. Strut suspensions are very sensitive creatures. Specs are one thing, but the real world is another. Tires are spin balanced to 55-65 MPH and cheap tires are sometimes not always round at these speeds. Have the run out checked. All this stuff will transmit into the steering wheel. Good Luck.