I just bought a one owner 2000 f150 with 89k miles. Everything works great except it idles a little rough at times, but doesn't stall out. Engine is the v8 5.4..not a 3 valve. Ive read where it could be the MAF, a vacuum leak, plug, wires, bad gas.........this owner had died and the wife gave it to her nephew to sell it. He's a AAA tech instructor and went over the truck before he sold it. plugs were changed out at 60k miles.I had it checked out at a mechanics shop that inspected it and said it was a good truck, found a couple of minor things that have been taken care of. after a day it started the rough idle. Again its only at times, Starts up good. Any suggesttions on where to start? I'm not a tech but willing to give it a go...thanks

 

Start by throwing some Techron in the gas in case you have dirty injectors. Then I'd start suspecting the coils. Could possibly be a dirty IAC.

 

Has there been a check made for code?
If no code, look at the long term fuel trim tables both banks for being shifted rich.
Then keep diagnosing until the cause is found.
You have to start some where and not run with guesses.
Good luck.

 

I pull the power brake vacuum hose occasionally and pour an ounce or so of Gumout with PEA in the line. It goes to the intake manifold and possibly helps clean the intake. It seems to help keep the idle smooth. I also put a couple bottles of Gumout for high mileage engines with PEA in the gas tank occasionally to help keep the injectors clean.

 

 

Look at the long term fuel trim tables for being shifted rich.
Do not put 2 bottles of additive in the tank when one will do for 20 gallon. Read the label.
To much upsets the air to fuel ratio.
The OX sensors are not designed to properly sense the excess oxygen the alcohol leaves in the exhaust gas after combustion. ( this is what they do, sense the exhaust result )
This, in its self, in excess, will richen up the fuel injected and can upset idle smoothness.
Good luck.

 

Thanks Bluegrass..I'll add one tomorrow and fill up the tank..will be my first full tank with it.

 

Did a little cigar smoke test yesterday and found a vaccum leak and fixed it. Where is a good place to hook up a hose where I can do a thorough smoke test to find any other possible leaks? Also..with or without engine running? Thanks

 

The bottles of fuel injector cleaner that I have noticed say that one bottle will treat "up to 20 gallons of gas". The tank is 25gallons. I always put two bottles in my tank.

 

 

Congratulations and thanks for sharing the fix.