Yup, my '87 16V locks by itself on occasion, with the key out of the ignition, or in, and with the ignition on or off. I can unlock the car and close the door, and it will lock itself in about 10 seconds. Just goes away by itself. I suspect the vacuum check valve, which I ordered ($8). I'll let you know if it works.
[This message has been edited by Webmaster (edited 03-21-2000).]