One problem related to starter has been reported for the 1998 Toyota Sienna. The most recently reported issues are listed below.
I came home and turned my ignition switch off but my 1998 Toyota van kept running. Turning the key on and off did not turn it off. I tried shutting it down with the ignition switch again and again and again. I tried turining it off again while moving the gear selector lever but to no avail. I begin to smell burning rubber. I lifted the hood and realized the engine was being turned over by the starter which was not disengaging and starting to smoke. Then tons of smoke began boiling off the starter. I disconnected the positive battery connection and the engaged starter stopped cranking the engine. Heavy smoke continued boiling from the starter for about a minute longer. I was very glad I was not inside the garage because I think the starter could have started a fire or the smoke would have smothered me.