So for the past week or two my jeep has been either losing spark causing it to miss fire which would lower the rpm's or there is something wrong with the fuel pump let me give you a discription, I pull up to idk a store for instance, turn off the jeep come back out and try to start it, just keeps wanting to start but nothing, kinda like you were on a incline and no gas is getting to the engine, and when it does start it doesn't stay idoling I think it's either spark problem, or a fuel problem, any one have any ideas? thank you

 

CPS (crankshaft posion sensor)

Read up on them. Very common problem and a easy fix.

 

My check engine light is on too, some people say check the vacumme line