Hey guys..

Every so often my truck would idle poorly (99 f-150 4x4 w/5.4), no codes though. Usually when it was cold and raining. Finally the CEL came on and gave a Right bank too lean code. Still ran alright until yesterday (raining) and I finally decided to make time to investigate. Heard a loud vacuum leak, found a hole in the PCV line to the intake and replaced it, then cleared code from the computer.

Motor still idles poorly... Came here to see what everyone says, and the search reveals typical fault is vacuum leak from PCV hose.

So if this was the ONLY problem, should the motor have run fine immediately after? Or does the computer take a few miles of drive time to correct itself?


If the MAF sensor is the next step, what would a good cleaner be for it?

Thanks for any insight...

 

ok so on cold days it will run poor or does it have to be raining at the same time? unhook the neg battery cable for about 10 minutes or so and then hook it back up and see what you get. for the maf, you can use a non residue electrical cleaner or maf cleaner. look behind the battery, there are vacuum lines behind it that the battery acid will sometimes eat.

 

yea like matt said check the vacuum lines by the battery, and clean the maf.

changed the fuel filter lately? what about spark plugs/coils

 

motor has 130K, new plugs went in at 90K with #4 COP... Fuel filter is ANCIENT... however there's no loss of power... Just poor idle on rainy days.

Sunny day today, still idles like crap though.. Fixed the PVC line vac leak, cleaned the MAF, cleared the codes, unhooked the battery to reset the computer.. Still idled like crap.. Went for a short highway drive, idles like a champ again... Go figure.

I fear the next rainy day.

 

Did you replace the rubber fitting on the end of the PCV lint that goes into the back of the intake elbow?

.

 

you should change that anyway....thats no good. even if that isnt the problem, it can cause problems down the line. idk what they say

 

Checked it... That fitting is actually fine...

It is running well again, so is it possible the computer just needed some run time to re-evaluate after I replaced the hose that leads to the side of the intake? That one was sucking some serious air....

 

the hoses from the intake to the TB?

 

There's a tee just above my PCV, one line runs to the back of the intake, the other runs to the side of the intake, just behind the throttle body... (on the large cast aluminum elbow that turns down to the main part of the manifold) That line is made up of a rubber elbow at the tee above the PCV, a hard plastic pipe, and then a 2" straight rubber tube to the intake. That 2" piece of rubber had a small hole.

There's a 3/8" coolant hose that connects to the intake just in front of this vacuum line, so I'd imagine 10 years of high temperature in this area caused that 2" rubber hose to fail.


While it still runs fine, I'd sure like to know if that hole in the hose was really the issue, or if Im in for it all over again the next rainy day. I even misted the engine compartment with a spray bottle to see if anything would act up and cause the rough idle... No luck...