I have 1999 lexus ls470 -- same problem -- ignition switch

Its usually NOT the lock cylinder on the 470s, its usually the housing. The cylinder is on the dash and points towards the engine. Behind the plastic dash panel (once removed) you will see it in fact sticks in an aluminum tube that goes down 2 or 3 inches, then makes 2 turns, left to attatch to the steering column, and right to attatch to the actual ignition switch. The gear and rod assembly that the cylinder attatches to that allows it to rotate the switch usually shatters in the middle and the key starts freewheeling because there is no longer any attatchment to any of the gears or springs or click points that youd usually feel as the rotational resistance. UNFORTUNATELY this is not a 5 minute job (If it was, cars would be a breeze to steal!). Youll need at least a lock cylinder housing (dealer stock em, they break all the tyme), and IF your cylinder is undamaged, change the housing (it bolts to the steering column and extends from column towards center console area where the ignition SWITCH is actually located). If your cylinder is damaged or the housing is so shredded you cant remove the lock cylinder by normal means...then youll also need the cylinder...and it will have to be recoded to the vehicle so the anti theft will allow the new keys/cylinder to start the car. If your old cylinder and keys are intact, then transfer them to the new housing and car wont even know it happened and should start up and work as normal. Some can be removed intact, some cant...depends on how yours broke.

Yea it sounds like your ignition switch has broke, the only way to fix the problem is to replace the ignition switch lock cylinder