Need Advice: Miss, low rpm stumbling

[EWest]

Hey guys, I am new to the forum and relatively new to the ZR-1 scene. I was hoping for some help with my '90. I have seen quite a few posts about engine hesitation etc., but none exactly like mine, so here goes:

There is a pretty severe miss during cold idling, and sometimes less severe while hot. At low rpm acceleration there is a severe stumble / hesitation up until about 3000rpm, when she takes off like nothing is wrong. WOT at low rpm usually causes severe stumbling and backfire through the plenum, but oddly on occasion she accelerates fine. The less throttle you give, the less severe the stumble seems. It seems that the lower the rpm the worse it is, especially in higher gears.

Idle is at about 800 rpm.

I replaced the fuel injectors with the rebuilt fic ones, and had to pull the plenum again to fix a vacuum leak in the intake. No change. Plugs and wires are new. I'm kicking myself for not replacing the coils while I was in there, but I did the "pull the plug wire and check the arc" trick and all seemed to have good spark.

I realize there are sensors etc. that I should test, but where should I start?

Thanks.