Cadillac Fleetwood Questions

I have a 91 fleetwood 4.9 FWD that occasionally will not ...

I have a 91 fleetwood 4.9 FWD that occasionally will not start.  All the electrical comes on but the motor won't crank.  Nothing.  Battery is good.  If it sits a while or I jump start it, it starts and runs just fine.  I have know idea?  ICM?  Relay?  Anyone heard of this?

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96 Cadillac Fleetwood Brougham: Hesitation, intermittent and rapid but only with airconditioner on.
Plugs wires and distributor have been replaced. EGR is OK. Mass flow detector clean. Air pump deleated as per TBS. Suggestions???