1997 Lexus SC300. 113,000 miles. Starter stays engaged and keeps cranking motor with ignition off and key out of ignition. Had to pull battery cable to disengage starter. When battery cable is reattached starter engages without key in ignition.

Could be: a) starter cannot turn the motor flywheel (motor frozen or jammed)
or b) the battery is weak (not enough power to crank the motor)

Turn the dome light on and see if it is bright, see if light diminishes completely when engaging starter (high current drawn by starter).

Try to turn engine by pulling the alternator belt with transmission in neutral to see if motor is jammed. Or engage in a high gear and push the car and see if motor turns.

If motor is not frozen, jump and boost the battery if you suspect weak battery and see if you have the same problem.

Try cleaning and tightening well the battery connections along with the battery wires to the solenoid and starter motor.

Bad connections and low voltage of 12 volts can result in this anomaly.

To check the starter: key off, transmission in park or neutral, brake set. Pull off the small wire to starter solenoid. Then use a small jumper wire from battery cable post on the starter to the solenoid terminal (can also use a small screwdriver to bridge those terminals). Starter motor should engage the flywheel and spin the engine. If nothing, starter motor or solenoid is bad. If starter works, check for power on the small solenoid wire, with key held in crank. Wire should have power, if not, check start circuit from ignition switch to solenoid-the neutral safety switch is in that circuit.

It sounds like the anti theft security feature has been triggered or faulted and locked the vehicle down so it won't start. If that is what has happened, the dealer can fix it for a substantial fee. You can tell if your truck has the antitheft system by looking at your ignition key. If there is a computer chip or resistor in the key, then you have the system. If not, then the problem is somewhere else. Check the battery cables to make sure they are tight and in good condition. Make sure the wires and cable are attached to the starter and tight. You can check for voltage at the starter by taking a long screwdriver and shoring across the battery cable where it bolts to the starter and the engine block. If the starter is getting voltage, it should engage. Do this with the transmission in neutral, parking brake set and ignition key on. If the starter engages and starts the engine, then the problem could be the starter relay. If the starter does not engage, but you do get substantial sparks when you short across the starter then,the starter is bad. No Sparks at all means the battery is not supllying voltage to the starter.

Seems to be a problem with the solenoid on the starter. After the engine starts, and you let the key go to the "run" position, the solenoid is supposed to disengage. If it stays engaged, it keeps the battery to starter contacts engaged. You have to remove the starter to get to the solenoid -- usually it is best to replace both the starter and the solenoid as a unit.

To start with a potentially cheap fix, try running 1-2 bottles of fuel injector cleaner through it to see if it's just dirty injectors.

After that, try checking the plugs. They're very likely 100k mile platinum plugs and are due for a check or change.

Starter solenoid probably.
-----------------------------------------------------------------------------
Sequence of Operation

NOTE: An overrunning clutch in the drive assembly protects the starter motor (11002) from excessive speeds during the brief period before the driver releases the ignition switch (11572) from the START position (as the engine (6007) starts).

1. The ignition switch is turned to the START position.
   

1. The starter solenoid (11390) is energized, creating a magnetic field in the solenoid coil.
   

1. The iron plunger core is drawn into the solenoid coil.
   

1. A drive lever and pin (11067) connected to the drive assembly engages the starter drive (11350) to the flywheel ring gear.
   

1. When the iron plunger core is all the way into the coil, its contact disc closes the circuit between the battery (10655) and the starter motor terminals.
   

1. The current flows to the starter motor, and the starter drive cranks the flywheel (6375) and the crankshaft (6303).
   

1. As current flows to the starter motor, the pull-in coil is bypassed.
   

1. The hold-in coil keeps the starter drive engaged with the flywheel.
   

1. The starter drive remains engaged until the ignition switch is released from the START position.
   

#1 is the stater with the solenoid on top of it.

The problem is either the starter solinoid (located on fender near battery) or you are not getting power to the "s" terminal on the starter solinoid from the ignition switch. If you follow the positive battery cable from the battery you'll follow it to the solinoid. Remove the small wire from the terminal marked "s" on the solinoid and using a screwdriver jump from "s" terminal (not the wire) to where positive battery cable connects to solinoid. (with battery connected). If starter doesn't do anything the solinoid is bad. If starter cranks then you are not getting voltage from ignition switch through "s" terminal wire.

overun clutch on starter is bad replace starter

Your starter drive is staying engaged. Either the starter has failed, or your ignition switch is keeping the starter engaged. Try moving the key back from "start" while the noise is occurring. More than likely, the starter is the culprit.