I'm new to this group. The problem might be a bad potentiometer.
Check:
http://www.ipdb.org/search.pl?any=corvette&search=Search+Database&searchtype=quick
Then download:
http://mirror2.ipdb.org/files/570/Bally_1994_Corvette_Manual_Amendment_16_9890.pdf
Right at the beginning it mentions the engine test procedure. A potentiometer is used to adjust the centering. It may be dirty or just a bad one.