Hello, the simplest cause would be if the throttle plate/bore has carbon build-up causing the idle air control valve to react more aggressively than intended and resulting in a stall. the next would be a inoperative idle air control valve. If so, it could be a defective valve or the computer control of the valve. Sometimes the distributor pickup coil/shaft/ polepiece in the dist will get weak and have low output ( less than 700 millivolts output cranking ) but I think you should start by cleaning the throttle plate and remove the iac valve and clean the pintle. you can also increase the minimum idle speed set screw SLIGHTLY and see if that helps. That will help determine if airflow is the problem or if you have dist or computer type concern. My goal is for you to be completely satisfied. If you feel the info I have provided was helpful, click the accept button so I will receive credit/payment for my answer. Thanks for using JA
ASE Certified Technician
ASE MASTER & ASE L1 ADVANCED ENGINE PERFORM RECERTIFIED. G.M. WORLD CLASS TECH. 22+YRS CHEVY DEALER