Mach 1 is absolutely right. Just set it to .98 and don't worry about it. There're only three things the ECM is looking for, closed throttle, part throttle, and WOT.
If you set it too high, your ECM may think you're at part throttle when you're really at closed throttle. That's not good.
The only time you should really check it is after setting idle. If you're idling high, you need to do something else to set your idle. Search on feeler gauge idle to find threads on the subject.
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351W 89 Mustang GT Convertible