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Couple of weeks ago I climb in the 04 TJ 4.0 and it wont start. Long cranking and it would some time catch but die. You could hold the pedal down and it would start and rev up but as soon as you let of the throttle it would die. Eventually it would settle into a rough idle and sometimes die while idling or driving if you let off the throttle. You could do the one foot on gas and the other on the brake and keep it going. I parked it overnight and boom it was perfect the next day and for the following couple of weeks until today. Same thing when my wife drove it today. I was out of town and came home this afternoon and started right up. Only thing I have done is replace the battery which was weak. Any suggestions would be greatly appreciated. Im thinking a failing fuel pump but thats a 170 dollar guess. Can a fuel pump act out intermittently like this.
 

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I'm having a similar problem, but I replaced the pump, sending unit, and the filter. No avail. I've been reading about the crank position sensor but I don't think it's that either. Just seems like there's back pressure or so etching blocking fuel from getting up to the rail.

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Spend the time to diagnose what you are not getting. Is it fuel or spark? Which one don't you have when it won't start.

Also the Idle Air Control Valve is what controls idle speed. If the valve is not working or the bore is blocked you will have all kinds of idle problems. Ditto if the throttle plate is not fully closing due to a build up of varnish under it.

Sometimes a simple cleaning of the valve and bore, and throttle body under the throttle plate will correct it. Carb cleaner and an old tooth brush work well.
 
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