AxJx

So my 99 xj 4.0 has been through alot. Recently, it threw the p0172 code for running rich. The o2 sensors had just been tested. replaced a bad thermostat, flushed heater core (still not getting any heat) new distributor cap and rotor, replaced MAP sensor,replaced bad idle control motor, and that's when it started actually starting up and idling without dying. It was running good but sputtering when the rpms dropped (say after going 55 then stopping at a light) but it wasn't stalling. Last night, it was doing the same thing but it ended up stalling on me about 3 times. then as I get back to the house (i was about 2 miles away) a loud hissing sound came from what sounded like the block (thinking maybe a freeze plug, haven't taken a look at all of them yet). I'm at my wit's end, gonna pull/clean the plugs again, check all the injectors for leaks (they're all 4 port and only have about 15k on them) Any ideas as to what's causing this?