1994 Buick Lesabre Stalling & Missing /Electrical?

Engine Mechanical problem
1994 Buick Lesabre 6 cyl Two Wheel Drive Automatic 150k miles

Hello ARH representatives,

My name is David, and I have a 94' Buick Lesabre (has about 150k miles on it). About 4 days ago on my way to work my engine started to miss and would shut off at low RPM's, not all the time. For example it would miss, miss, miss then shut down or shut down randomly while I was driving (this doesn't happen as often). But in some cases I'll be driving for a half an hour and not have it miss once.
I have to shift (automatic) into Neutral and rev up the engine a little to keep it running. I changed all of my spark plugs thinking one was bad, but it is still having the same symptoms. I took the Buick to a well known, well trusted mechanic to see if he could find the issue. But he wasn't able to get the error codes, he said he didn't have the best equipment to get them. An he could replace valves etc. But it would be throwing money down the drain not knowing what the error is. So I picked up my car today and took it to autozone for a free diagnostics test. The handheld device he used was only coming up with a error, like it wouldn't read. He tried another, but same, handheld device and it would not read. Any help would be greatly appreciated, I'm stumped