Starts with high acceleration. Wont' turn completely off and diesels instead.

What is your question?

When starting the engine, the engine accelerates at high speed until I turn off the ignition. But then it doesn't turn off completely. Instead it diesels. It diesels only when being forced to turn the car off when it has started at full speed acceleration. The problem is only occasionally. 91 Buick Century. 3.3 automatic.

How long has your 1991 Buick Century had this problem?

2-3 months