Update: I tried Oscar's suggestion of turning the key from off to run several times before cranking. Following are the results:
Initial Conditions: Had not started car for about 32 hours. (I didn't try to start it until after turning the key from off to run five times for the first time.)
turned key from off to run five times, then turned to start. Car started immediately without hesitation, and seemed to have fair power.
turned off car. turned key from off to run five times, then turned to start. Car cranked/turned over, but didn't even come close to starting.
repeated this procedure twice, with identical results.
So it was only after the first cycle of turning the key from off to run that the car started; after that, it was ineffective.
(It could very well be, by the way, that the car would have started the first time, after only turning the key once, but I didn't try this.)
Can anyone interpret these results for me?
(I wanted to clarify that my engine does not run rough or idle inconsistently; it is just that the idle sounds very low-powered compared to the other Grand Prix. It also does one of three things when I try to start it: crank but not start at all, crank but start only after a couple of seconds, or crank and start immediately, albeit with low power. I am getting the impression that it only starts immediately when I have been running the car for a while soon before starting it again.)
Thanks!