It's a combination of the load on the motor and the engine speed. When you have a vacuum leak at high rpms, it is less noticable. At low rpms, it is much more difficult to keep your engine running because of how slow that it is turning. It kind of like having a wild cam. They don't have much vacuum and idle like crap.
I doubt that it only applies to ATXs. It just that because the ATX never truely disengages, it makes the problem easier to spot. (the intake gasket leak) when you engage the clutch on a MTX Zetec, there is no load on the motor besides the accessories. (alternator, waterpump, etc.)
BTW, for you guys that want to replace yours, it is a full weekend project. You have to take off the alternator, alternator bracket, and passenger motor mount. You will learn alot about your Zetec in the process.
For the Pre-98's, also plan on cleaning your intake. The EGR really gunks it up and robs you of power. Soaking it in 8 gallons of Castrol Superclean overnight makes it as clean as new.
BP
