WOW what a vac leak!

[lightninggen1]

Hey guys, I have a 95L and I lave it but this morning when I started my truck it wouldn't idle. and I could hear a nasty vac leak. I had to drive it today so I turned my throtle stop screw about 1 round in and got an idle. Now I need to find the leak.I looked every where, I checked every line and fluid tested the gasket surfaces that I could get to.It is loud and sounds like its coming from the box on the upper intake. I dont think my intake has ever been removed and I have a BD11 with the 6# pulley.{and no its not my blower I hear}I even went as far as to remove vac lines to find the leak and no luck.if anybody has ever had this problem I am open for ideas.

Oh yea and why a loss of idle and not an increase in idle RPM?

My brain hurts Thanks for any help

 

[Litng1]

Did you check the vac tree on back of intake?What about the lines under the upper?Maybe FMU vac line.

 

[DAVE94LIGHTNING]

Check to make sure the PCV valve is sitting snug in the rubber grommet in the back of the lower manifold.

Good luck

 

[lightninggen1]

I have checked the vacuum tree and the FMU with no luck and yesterday I checked the pcv valve and it was fine. I think I will check everything again today after work and see if I missed any thing

 

[Nick Wilson]

Take a can of starter fluid and spray under your hood. If the engine revs when you spray a certain spot you have found your leak.

 

[gasguzzler]

There is a vacuum line kind of hiding under a wire harness that goes from left to right along the top of the firewall. I had that one get pinched. I could only make about half boost and it was really doggy then. - Brian

 

[lightninggen1]

Thanks everyone for your help I found it. well kind of, The problem was the IAC motor had locked shut thats why I lost idle and that forced more air through the BBK throtle body causing a very loud wistle. Thanks again for all your help

 

[SVTHOTROD351]

Hey i'm having the opposite problem...mine idles fast...and now its shifting hard...i dont mind the hard shifts..but i want to make sure that there is not a problem ...i first thought a vac line had come off and the comp was trying to fix by speeding the idle up,,so i checked the lines and found my pcv had poped out of the gromet....so i pushed it in....wow was that a big mistake...the valve was bad...so it ran like crap...so then i changed the valve and its running good now just fast..yesterday i was at a light and with it in drive and my foot on the brake it was at 1800, then in -n- it was 2300...i parked and went in a store and when i came out it was back to where it was before...about 1300 in -n- and 1100 in -D-....

 

[RED314]

Run away idle

I found and corrected a problem like this awhile back. The upper intake gasket had somehow went away

I think the upper just vibrated loose and created a major leak. New gasket, problem fixed:tu:

 

[lightninggen1]

Hey SVTHOTROD,
I have seen IAC motors do this befor but not often. when they do stick open a little it will cause high idle and not allways at the same RPM..Here is a quick test next time it idles up stop ant simply tap on the IAC motor if it is hung open it will drop to it normal idle when you do this. You might have to give it a good tap but dont damage it or your T-body...we dont want to brake any good stuff. I dont think its a vac leak becouse a leak will not just go away by it self.
But keep an open mind dont focus on one idea I am a driveabilty teck and so many times I have screwed myself thinking closed minded

Good luck
Jeff

 

[SVTHOTROD351]

Hey..

Thanks for giving me a place to at least start to look ...i will keep you posted as to what i find....thanks again :tu: :w