Get a light back there and see if the injector o-rings are leaking...
I just had someone around here who was having issues when his injectors weren't sealing correctly all the time. Slightly different situation, but the symptoms are similar.
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Kinda sorta, yeah, no?
'02 Black GTP - RIP 03/03/08 ||| '06 Black G35 MT6 - Stock ||| '73 Chevy half ton(resurrected)