im ready to torch my 95 f150 5.8L. ok before it left me stranded i noticed it was idling rediculously high one day and later that night went to go home and would not start. towed it home beeen workin on it since. i changed the idle air control valve but the truck will not start unless i use either or starting fluid. once it starts though it will stay runnin but still idles high unless i blank off the iacv. so i gather there is something tellin the computer that there is alot of fuel to open the iacv when in fact there isnt enough fuel to start the truck. ive checked the fuel pressure to the rails and im getting no codes. what can be the problem?

 

Vacuum leak.

 

ive checked all my lines but ill recheck

 

towards the back left of the engine, there should be an large upsidedown L vacuum line. with a metal fitting into a rubber hose. It seems i change that specific line once every 5 months. I would definatly check that one. Truck idles just over 2k whenever that line is busted.

 

could you be a lil more specific? the back left lookin at the engine from the front or from sitti in the truck? and about what size is the line? i couldnt find what you were talkin about by just lookin or feelin around.

 

Sounds like he is talking about the PCV hose and the PCV valve is located at the back right (drivers right as setting in the seat) of the engine and goes into the right bank valve cover. The hose source is the upper intake on the drivers side.

The only other large vacuum hose is the one going to the brake booster. Make sure the brake booster diaphragm is OK or it can it can have the same effect on the engine also.

 

yeah ive cheched all that plus if there was a leak the iacv wouldnt be opening up all the way. i believe something is telling the computer there is alot of fuel and i need more air hence the iacv opening all the way. im just not sure what. i might have to try some O2 sensors but i really dont wanna just throw parts at it. no vac leaks all been checked and re checked. really need schematic for wiring of engine control systems and sensors.

 

Check for leaks around the upper intake gasket. Check the TPS, I know it sounds ridiculous but I've seen this be the problem on several of these engines.

 

What makes you sure the IAC is all the way open? I mean how'd you verify that?

You unplugged the IAC when the engine is running, idle dropped down to near normal?

 

Unplug the IAC. If the idle returns to normal or stalls then it is not a vacuum leak issue. Something is telling the computer to open the IAC too far.

 

You beat me to it.......

 

Sorry bout' dat!

 

i have blanked off the iacv and the truck idles normal. but only after i get it started with either. just unpluging does nothing which is why i stated something is telling the iacv to open too far and restrict fuel. not enough fuel on start up but once i get it started with either it will run normal with the iacv blocked off and without blocking it off it idles at two grand.

 

oh and i have already replaced the iacv. and im assuming the tps is the throttle posision switch or sensor??

 

please read in entirety before commenting please so i dont have to repeat myself anymore. appreciate all the input though.