IWantaScoobyNow

I need some help from some techies.
My my93 wrx has a a flat spot at around 3-3500rpm.
The car has recently had its 90k service and has not been right since. All the coils, plugs etc have all been changed.

Weird thing is my local specialist cannot isolate the problem as it will not hesitate with their laptop linked into it on test drive. Therefore they cannot pinpoint it.
It will do it without the laptop on it, although it is not frequent but just bloody annoying.
Obviously they are working on it as I speak but I thought that maybe someone may be able to suggest something that they havent thought of.

Any help greatly appreciated.
Dave