my 1991 300 ZX runs on 5 cyl. Could it be the ignition control module?

Check compression, check injectors, and then check the module. The only way to really see if the module is bad is to replace it with a know good module (aka a new one) and if that fixes the issue you know it's the module. Good luck.

its probably the injectors. i had a few go on my 91 a couple years back and they were a bitch to trace down. first step is to make sure they all ohm out correctly

BTW, injectors should ohm between 12-14ohms Also, if the injectors pass the ohm test, then test the coil packs, if they check out ok, do a compression test.