Help please..Can't turn the engine off with the key.

[Chippar]

How do I fix this...(I have a 2001 AUII Sedan with 40000 ks.) I can turn my ignition key off and even remove it from the switch, but the motor keeps idling away.
I have an Auto and the only way I found to stop the motor was to disconnect the Idle solenoid to slow the idle right down and then take off a plug lead and the motor will stall.
I noticed that the ignition lights were still on in my dash indicating power was still flowing, so I disconnected the battery lead to de-energise the coil.
Has anyone heard of this problem or know a fix for it? Please help.

Chippitydip.