94 mustang idle/battery problems

Here is a link for a checklist that will show you how to check for codes, pay attention to the highlighted stuff for 94-5 cars, https://www.stangnet.com/mustang-forums/threads/how-to-pull-codes-from-eec4.889006/
As for the fuel pressure you should be able to get a fp gauge from the local auto parts store, some will lend you one if you have a credit card, if not you can buy an inexpensive one and temporarily attach it to the Schrader valve, I say temporarily because if you leave it there the vibration will eventually cause it to leak and you don't want that.
There are more helpful stuff in the technical/how to forums that members have contributed to over the years.