out of all three of my trucks this is the only one that has a vacuum on oil cap if you remove the cap idle speed drops any clues?

 

My first thought is pcv valve stuck open or breather line collapsed so stuck closed. Or the reverse? Either way... check those 2 things. They are the only things I can think of to cause vacuum in the crankcase. Usually people end up with pressure in the crankcase... so this is odd.

 

that was my firs thought as well i checked and clean pcv valve if i remove it the vacuum goes away. the hose beside the oil fill cap that run to throttle body also has vacuum. but the throttle body does not at that port. the port on the pcv valve has vacuum. i have since replaces both hoses and new pcv and no change. truck also dies if you rev to 3500 and just let off pedal. but if you bring it down slow you can keep it running it stumbles but doesnt die

 

Got any pictures? Got me curious now.

 

i dont have any just a stock 2.5. The oil cap and the vent hose to tb have vacuum got me stumped

 

My 2003 2.3L has a fairly strong vacuum on the tube that goes from the intake hose/tube to the top of the valve cover( runs beside the fill cap). I assumed that was normal because it should be pulling air in through that and then out through the PCV to the intake. But when I pull that tube off, the RPMs drop on mine.

 

the rpm drop on mine to. my hose goes from right behind the oil fill to the side of throttle body between the throttle cable and air intake hook up. my 2.3 i have doesnt have vacuum but the hose runs to the side of air intake. we let propane blow in threw oil cap and truck rev up alittle. so to a point that would kinda make you think that if it can make it to combustion chamber to burn that oil could as well? we have replaced all the line and pcv valve so kinda stuck on what to do in process of checking valve cover gasket. (does lose its vacuum when you take pcv valve out so i dk if that the vacuum source or just makes a place for it to go)

 

I could have this incorrect, but if I understand correctly the fact that it goes away when you remove the PCV proves that it is coming form the intake. The intake creates the vaccuum, so the vacuum at the PCV valve is passed through to the crankcase and the valve cover. Like this picture shows

http://www.agcoauto.com/content/imag...g_moisture.jpg

So I guess it is possible your PCV valve is stuck open. That would cause the vacuum to be too high at idle.

 

At first what i had thought pvc valve so i changed it and hose sprayed there ports there open the truck also dies if rev past 3500 im thinking that fuel filter all sensors have been checked ..guess im just gonna run with it unless this vavle cover gasket fix it