I have the same EXCAT issue with my 1995 S300. What I have noticed that:
A. Problem is intermittent
B. The engine dies when I get off of the Freeway (after going really fast, if I suddenly stop, chances ARE THAT MY ENGINE DIES).
C. After the engine dies, I turn the car off then on and everything fgoes back to normal (I guess that's Control lt Delete to reboot my car!)

Any advice appreciated