Miss when cold and at idle
 

I have a '95 XJ with a straight-6 that has developed an issue. I am not very familiar with fuel injection so I am in largely uncharted waters here. It has always had a slight miss at idle since I bought it (nothing worth writing home about so I thought nothing of it). Recently however, it started to idle poorly and miss fairly significantly at speed. I put in some fuel injector cleaner and it seemed to help, it still idles like crap and misses when it is cold, but once it warms up, it is back to only a slight miss at idle (not as slight as it was but still not significantly noticeable).

Has anyone encountered this before? Things I have thought of are vacuum leak and timing but I cannot find any sort of vacuum leak and I could not find a spec to check the timing against. Plugs, wires, cap, and rotor are all new as of about 2k miles ago.