2003 Explorer has rough idle


jwc.enterprise
10-20-2012, 02:44 PM
4.0 SOHC cranks once no start, then starts on second crank. 104K miles and used to idle very smooth, now mildly rough and sometimes upon stopping the rpms will dip down to almost stalling but not everytime. Any suggested areas to start my inspection will be greatly appreciated. Also just had the fuel pump replaced.

Also... Seafoam? Is this really as good as it sounds, I mean it can be used on anything, except cereal!

shorod
10-21-2012, 10:32 AM
Welcome to the forum! The place to start your inspection should be with a fuel pressure tester on the fuel rail to see if the fuel pump is properly priming the system when the key is first turned to the Run position. Next would be to perform a tune up - spark plugs, plug wires (if not CoP), air filter, and fuel filter. SeaFoam works great as a cylinder decarb, but I've not tried it in the fuel tank or in the crankcase.

Your symptoms sound consistent with a weak fuel pump that is unable to properly pressurize the fuel rail with a single cycle of the key. You could test this theory by turning the key to the Run position (but not the Start position), leave it there for about 2 seconds, turn the key off for about 5 seconds, then turn to Run again, then try to Start the engine. If it consistently starts easily this way it would suggest the fuel rail is not building sufficient fuel pressure, either due to weak pump, a leaky injector, or a restriction such as a dirty fuel filter.

-Rod

jwc.enterprise
10-21-2012, 01:37 PM
Thanks for the suggestions! I'm going to start with the tune-up/filter change since I KNOW it hasn't had the 100k service. Thanks again and I'll post my results.

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