Bad computer

[RGuzz]

Hello,
Rarely list but have what I believe is unfortunately a bad 
computer...TAP chip age unknown has been missing and bucking 
intermittently. This is a new problem ie a few months old. Have been 
working on this problem with a knowledgeable Audi repair 
facility...swapped coil, plug wires, plugs, fuel filter no change then 
dropped in a stock computer and so far (one week later) all is well. 
I'll leave the borrowed working computer in for a while longer to be 
sure.
So I may need a computer. Can they be further tested to isolate the 
problem? How do we know it isn't the chipset itself? Does IA have a 
bunch of these? Anyone have a spare for sale? What should I be thinking 
about next?? Car with 175k miles otherwise runs perfectly.
As much as I love this car it has cost me a fortune and this is my 
second one...
All advice appreciated.
Richard