You can tell which switch is which by the wire colors. If your car does not require the clutch to be depressed when starting then it is w/o the Interlock Switch, but has the Clutch Switch. Clutch Switch has a Black wire and Green/Black wire on an S5. Interlock wires would be B/R and B/G. Since your car was an auto it is not apparent which switch was installed. And voltage from the Clutch Switch does not run to the starter. Interlock, yes.

 

We dont seem to have the interlock switch and are using the clutch switch as the interlock.

 

To provide closure for anyone who runs into the thread from a search, running 1Q to the clutch switch and from there to the ground does seem to solve the dying when decelling problem.

Since our car was originally an AT there was no line going to 1Q (clutch switch). So I de-pinned 1R (neutral safety switch) and pinned it into 1Q and cut it about 4 inches away from the ECU for easy extension with a new bit of wire.

Thanks to everyone for the help and advice.