I think it may be worth your while to crawl under the car with a flashlight and your tools. -this may shed some illumination on the subject.

Last Feburary, a friend of mine was wondering why he didn't have as much power as he was expecting on his '89 740 Turbo. It turned out that his Air Mass Meter had blown it's Platinum wire, and this caused the Fuel Injection system to default to full-rich, and the extra hydrocarbons in the exhaust were more than what the cat was originally designed to handle, and this caused it to heat up hot enought to melt the ceramic core, and the extra heat started passing through the heat shield and melted the bottom of his back seat cushion.

Once you've identified a failed part, follow the cause & effect sequence back until you find the original culprit. In many of the vehicles I've worked on it's turned out to be a bad thermostat (airbox or coolant), a blown gasket or o-ring, or something on the maintance/service schedule that's been neglected (fluids, filter, inspection/check of a wear part, etc).

Also, there's a lot of helpful information in the 700/900 FAQ on this board:
http://www.brickboard.com/FAQ/700-900/

If you've got a new-to-you, I'd start right away on catching up on the service schedule (unless you have reciepts that show specific items are current). Also, a bad airbox thermostat under the air filter ($10) can cause your Air Mass Meter do die (prolonged exposure to hot intake air), and thus the sequence of events starts... Also change your O2 sensor if it's older than 5 years (more info here for regular cars, and here for Regina system cars).

God bless,
Fitz Fitzgerald.
--
'87 Blue 240 Wagon, and my 240 has 240K miles.