Was driving along the other day when I smelled burnt plastic in the cabin. Looked under the car and found that a plastic bag has stuck to the cat converter and got fried; it eventually burned itself away.

Well, a day later the check engine light comes on when I'm at a stop, but disappears when I hit highway speed.

Any clues what's going on here?

Thanks for any replies!

~Paul

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'91 300E, 199k