Rough running XJ...went home on the flatbed

I drove to my highschool, Jeep ran perfectly and 30mins later I went to go back home. I started the jeep and it fired, however it ran horribly, almost like a carb'd engine running like crap. The RPMs bounced from 0-250 very erradically at idle, and pushing on the gas did not change anything ( RPMs did not go up), and yes, all of the throttle linkage is fine. There was no smoke from anywhere. The engine is getting air and gas, so this seems to me like an ignition issue. The plugs, cap, and rotor are probably about 1 year old. The fuel injectors are almost new and are in great shape. Could this be the CPS or something? There was a large amount of some blackish/browinsh oil under the jeep in the parking lot ( not thick like engine oil though, kinda greasy and no smell to it), however I'm not sure if it was there before I parked or not so I'm not sure if its mine. The coil is a new autozone unit within the last year. Oil was recently changed and analyzed by blackstone labs, the only significant issues they found was a little more than average fuel in the oil and some excessive iron and lead. For the last few months the harmonic balancer has shown some in/out movement, which worried me. I was thinking timing belt maybe, but theres not way the engine would run at all if this got messed up right? I'm just trying to include anything that might help solve this problem. I'm going to pull the plugs and all the ignition stuff on Thursday when I get some time off from work. 89 XJ 4.0, AW4, 185k. Thanks for reading all of this and for any suggestions.

UPDATE!!! After doing some reading on CPS related symptoms I thought this might be the problem. I read something about if the CPS was shot it would only effect the engine when warm. Anyway, now that the Jeep has been sitting in my driveway for 2 hours and has totally cooled down, I went to start it. It fired and ran beautifully. Does this back up my idea that the crank position sensor needs to be replaced?