I have a 2001 F150 with the 4.6 engine. I get an intermittant drop in the idle from 700 RPM to about 500 RPM. The computer catches it quickly and brings the idle back up. It might drop several times and clear up or it might not happen at all. Seems only to happen on a hot engine, never when cold and in gear, if in park or neutral seems to idle ok. Changed the idle air control valve but no different. Runs fine except for the idle dropping when stopped.

Never get a check engine light, and no codes from the computer when I had it checked. Any ideas would be appreciated. Could this be the vapor management valve turning on?

 

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Have you replaced the fuel filter lately? What condition is the air filter in? You might try cleaing your MAF sensor also. Do a search for instructions on how to do that.

 

I'm having the same problem with rough idle and a miss. I'll be the first to admit this truck has not been maintained as it should, 120,000 miles without a tune-up and the only major breakdown was last week, lost a tranny.

I bought Motorcraft plugs to install tonight, but can't for the life of me find any help with the fuel filter. I'm a very busy fellow that doesn't work on engines unless I have to, which means I'm broke now and need to fix this myself. $1250 on a tranny will do that to you! LOL

So, what else besides plugs, wires and a fuel filter should I replace? Thanks for the help.

Oh, and I hope I didn't crash your thread too much. Our problems are similar so I thought this would be a good place to start.

 

Replacing the fuel filter isn't so bad, once you have the proper tool. The part store sells cheapo versions of the tool for 10 bucks or so. I don't remember it's actual name, but the tool is used to de-couple the filter from the fuel line.

You'll find the filter tucked up agains the frame about half way down the drivers side of the truck. Relieve fuel system preasure, and then use the tool to disconnect the filter from the lines. When you install the new one be sure the arrow points in the correct direction.

 

replaced fuel filter no help. Any more suggestions?

 

wltrmart, check your pcv valve, or just replace it for $4 if truck hasnt been maintained. Is air filter clean? check for vacuum leaks and whether the hoses are tight. Make sure the intake air assembly from fender well to throttle body is tight i.e. no air leaks. If you know the maf is clean, consider TPS (throttel position sensor). Personnally i'd vote for a dirty MAF. plenty of threads on how to clean and it is easy to do.

 

I'm having the EXACT same problem with my truck. Did you solve your problem?

 

Having the same problem here too,, rough idle when at a stop, no check engine line, replaced the IAC, cleaned the throttle body, air filter, vacuum leaks, pcv valve. The last thing is the fuel filter and the very last is the plugs and/or coil packs. Would a loose boot from the coil pack also cause a "light" miss or rough idle?