Hi @Swan55
I have, this very moment, just had the very same experience as you had. The starter on my 1999 LS400 has been playing up as of late, often only providing a click instead of a full start.
Then for the first time, on this cold January evening, I started her up and to my disbelief I heard the starter keep cranking. I proceeded to remove the key from the ignition, however to my dismay, the starter motor continued to turn.
Luckily, I remembered that Lexus equipped these fine motors with a small tool kit in the trunk, so quick as a flash I grabbed a spanner and disconnected the battery.
Now I am looking at replacing the Solenoids with the kit listed on eBay. Tell me, did that solve your issue? A mechanic said that a safer bet would be to buy a new starter motor entirely however I would rather save the pennies and help this green earth by repairing/refurbishing my existing unit instead, if possible.
Kindest regards,
Jack