Re: Final Question on 98 Taurus still confused.
The TC is a self contained unit and shouldn't make the vehicle run rough. If the TC is broken internally, then it can cause some problems, but you wouldn't be able to drive the car if it was in fact broken, or a part decided to fail.
Don't forget, the car is going on 12 years old. Rubber vac lines can fail and rupture easily enough. I spray all mine down with a silicone spray to help prolong the life of some components, but really I'm just putting off the inevitable of having to replace parts no matter what I do. If you have the AX4N transmission, it's a built a bit better versus the AX4S transmission, both were used in Taurus manufacturing. My '99 was lucky to get the AX4N which has better reliability, and to date I have had no trans trouble in the last 126K - I run Amsoil ATF synthetic which no doubt helps prolong life.
If the vehicle is vibrating enough, who knows, it could have loosened a vac line and it might have come in contact with a hot engine component causing a slow leak. I haven't had any problems other than a seat belt issue (covered under warranty in 2000).
'00 Durango R/T 360ci 290hp (modded); 138,500m
'06 Pontiac G6 GT 3.5L 220hp; 44,000m
'12 Chrysler 200 Limited 3.6L 283hp; 13,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!