1994 Buick Lesabre car cut's off

PCM goes into closed loop approximately after 30 minutes with engine running. The underlying cause might be a bad oxygen sensor signal, airflow sensor signal or MAP sensor signal that is upsetting the air/fuel mixture.
If a problem seems to occur only when the engine is running in closed loop that would tell you it’s probably a sensor or PCM-related issue. The strategy here would be to look at some of the key sensor inputs such as coolant sensor giving wrong information to the pcm, (coolant temperature may not change when it should after 30 minutes)
either the oxygen sensor , the Map sensor or the coolant sensor is the problem.
If the sensors turn out to be good, check the ignition

did all you said to do and that did not do it.
what's next??

randytyler44
Intermittent problem is not easy to diagnose,
I believe there is a loss of important sensor signal, the crankshaft sensor might be the one .It is located under hood, passenger side, lower engine area, rear of crankshaft pulley, mounted in engine block. if the crankshaft is good, the ignition module may overheat .

Happy holiday