pcm not communicating

95 firebird pcm will not communicate with scan tool or if it does it has bogus readings like temp being 176,500 degrees or mph goes to 157,985 had car several different places can't figure out any info would be greatly appreciated

Well, is the scanner for OBD I, OBD II, or both? Because the 95's have OBD I, but come with the OBD II socket under the dash that you would normally hook a scan tool to run for codes. What kind of scanner are you trying to use?