[Quicksilver]

The DME Test Plan is probably the least recommended suggestion and it should be the first thing suggested for these cars. (Replace, replace, replace = fail. Test, test, test = succeed.)

Lets look at the physical conditions where the issue is happening:
- Low RPM
- High vacuum
- Low fuel flow

The fuel is fed by an electric pump so it has a fixed supply capability. If will run at high RPM under load then there isn't a fuel supply issue at idle. (Over pressure could be an issue...)
A spark jumps easiest in a vacuum and as pressure rises creating a spark becomes much more difficult. The higher the RPM the less time the ignition system has to generate the spark energy. If it runs under throttle at higher RPMs then idle wouldn't be a problem.

The biggest possible issues for rough idle would relate to the fact that idle is under a high vacuum condition. Look for vacuum leaks: Hoses, intake manifold gaskets, etc...

Other lower percentage issues? Broken head stud could cause an issue but you should be able to hear that kind of leakage. Dripping injectors could cause more idle issues as opposed to high RPM problems.