Even though this thread is from a few months back, I want to add that my car has just started doing this today. The wiggle test indicates the connection to the ICM, as when I barely tug on it, the car shuts off like the key was turned off. So +1 for the wiggle test.
96 9c1 Caprice (Former Ada co. (Boise Idaho) Sheriff's Office)
Afterburner headers, 2.5" catback w/Flowmaster 50's, egr/air/evap system gone, homemade CAI, TB bypass, 160 t-stat, meziere ewp, pcmforless tune, UMI rear UCA/LCA, moog 7268 front springs, energy suspension bushings, 'The Jetsons' roof antenna, Z28 cluster, driveway paint job.