94 Buick LeSabre hesitates or stalls

My 94 LeSabre runs well and smoothly, except: Almost always after it has run for a while and therefore has wormed up, it will hesitate as if running out
of gas or spark plugs aren't firing. It kind of stumbles. Sometimes the engine stops for half a second and then works OK again, other times it does this several times in the space of 2 or 3 seconds, then it will work OK. Rarely, it will stall when stoped at a trafic light or starting to go from it. Even more (very) rarely, it will stop when going. However, it will always start right after the stalling and work OK.
A month ago I replaced the EGR because there was a trouble code present. It's OK now. The fuel presure is OK. No error codes present. Several days ago I cleaned the back of the ignition module (under the distributorless ignition coils?) and for 2 days I thought the problem was fixed, then, it happened again.
Any ideas on what may be causing this?
Thank you
Antonio
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Alpha One wrote:

Possibly the crank sensor is going bad. It's about the right age to do so. Could be any of 27 other things though.
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I replaced the crank sensoir about a month ago. The car already had these symptoms. No luck.

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Alpha One wrote:

Mine - crank sensor. when you come to a stop, the engine bogs down and rpms go down. With a flaky sensor, it overcompensates and your rpms drop even further.
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Might also be the Oxygen sensor cycling slowly. I've had this on another vehicle -- usually easy and inexpensive to replace

run
out
does
from
days
it
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