Idle And Vent Problems

[Cannon77550]

Hey guys, so I picked up a 95 gt with the 5.0 the other day for $1500. Mostly stock except headers and flow master mufflers. She aint perfect but is definitely fun to drive and will be a long running project along with my daily for now. It seems to idle somewhat high and a little sporadic. Between 900 and 1000 on the stock tach. I do plan on going through the sticky on surging idle tomorrow and having my codes run. But I also have issue with my vent control not working and I feel like they may be connected due to a vacuum failure somewhere. Regardless of the dash setting I get equal amounts of air from the dash and defrost, no floor air even when on floor setting. I dropped the glove box and pulled the stereo and checked the lines in the dash and everything looks fine. Under the hood I did notice that a vacuum line on the passenger side fire wall was pretty rotted and flimsy but wasnt broken, but as flimsy as it was it wouldn't surprise me if it is collapsing under vacuum. It was connected to a small black canister with a plug in goin to it. From what I've gathered thru the forum that is a purge valve of some sort... I think to do with the fuel system. I've had a hell of a time finding a good picture or drawing of the vacuum system if anyone could link one that would be awesome. Searched SN but maybe I'm wording my search wrong but keep coming up with foxbodys that has a vacuum tree and I don't have a vacuum tree that I can find anyways. Tomorrow I'm gonna replace the two hoses I saw that were rotted around that canister before I start working through the sticky on surging idle but I don't know if that'll fix either of my problems. Any advice would be awesome TIA.

 

[Chythar]

The vent controls in the dash require a proper vacuum to run, and this is supplied by a tiny plastic hose that runs along the firewall in the engine bay. It starts at a vacuum tree in the driver's side corner, then across the pinch weld on the firewall, then goes through the firewall on the passenger side. Somewhere in that hose is a crack.

The purge valve you see is called the CANP - canister purge valve. It takes gas fumes from the charcoal canister in the passenger fender and vents them into the intake manifold. I would replace all cracked hoses before going through the surging idle checklist, as a vacuum leak can be the cause of a high idle. Also be aware that any hose that is a little loose on either end is also leaking vacuum, so it should also be replaced.

 

[Cannon77550]

The vent controls in the dash require a proper vacuum to run, and this is supplied by a tiny plastic hose that runs along the firewall in the engine bay. It starts at a vacuum tree in the driver's side corner, then across the pinch weld on the firewall, then goes through the firewall on the passenger side. Somewhere in that hose is a crack.

The purge valve you see is called the CANP - canister purge valve. It takes gas fumes from the charcoal canister in the passenger fender and vents them into the intake manifold. I would replace all cracked hoses before going through the surging idle checklist, as a vacuum leak can be the cause of a high idle. Also be aware that any hose that is a little loose on either end is also leaking vacuum, so it should also be replaced.

Right on man. Tomorrow ill replace some hoses. Thats probably why i couldnt find the vacuum tree. I have an alarm siren mounted up by the drivers side strut tower. Its not operable though so im just gonna pull it to allow me to get in there and try to find this leak and replace hoses.

On those hard plastic lines is it recommended to buy new ones or can i get some small rubber hose to replace it? Or should i just splice it? I just know on my old f150 those little plastic ones get brittle as hell and tend to just break next to the splice so id rather just replace it totally if possible.

Also what is a normal idle on the 5.0 HO? 650-700?

 

[Chythar]

On those hard plastic lines is it recommended to buy new ones or can i get some small rubber hose to replace it? Or should i just splice it? I just know on my old f150 those little plastic ones get brittle as hell and tend to just break next to the splice so id rather just replace it totally if possible.

Well, replacing the whole hose means getting behind the dash to find the other end, so most folks tend to splice it. If you can find a rubber hose that's a similar size, I'd say go for it. Just remember that a hose that's too big won't provide enough vacuum and your HVAC system might not work right. If they're close enough you should be OK.

Also what is a normal idle on the 5.0 HO? 650-700?

Something like that, but each engine is different. The Surging Idle Checklist also tells you how to reset your idle, once you've fixed all the other issues.

 

[Cannon77550]

Been lazy today but did go trace the ac control line. Didnt take long to discover it was bust right at the base of the boot off of the vacuum tree. Anyone have any recommendations on a fix? There isnt enough sticking out of the boot to splice too.

 

[General karthief]

Rubber vacuum line.
I think there is a way to repair the plastic line at the boot, I've seen it done at the shop but can't remember how it was done, maybe a repair kit?
Check out the 'help' section at autozone or O'Reilly s
I would just use rubber vacuum hose, one size to fit the nipple then a smaller one to fit the plastic line, just make them short

 

[Cannon77550]

So i reconnected my vacuum line for my ac controls and the one for the CANP. Found out the line goin down into the fender from the CANP was totally rotted off so i just capped it on the canister side of the valve for now. Mainly because i didnt feel like pullin the tire and the fender shroud to reconnect it. That brought my idle down to between 800 and 1000 and smoothed it out some but it still surges between 800 and 1000 and when it idles up i hear a click from under the hood somewhere. Fixing vacuum line also fixed my hvac controls but defrost still doesnt go total defrost i can feel air from the dash still. But it blows on the floor now. What would cause the defrost not to switch all the way over?

Also pulled codes and the only code besides the 111 i get is 564 during key off engine off. Looked it up and from what i can gather that it is electro dive fan circuit failure. But i can hear the fan run during the test... starts slow and speeds up. Checked fuses for it and they are ok too. Could it have to do with my overflow tank sensor being unplugged? Overflow tank has leak and wont hold fluid so previous owner unplugged it to turn off dash light.

But i gotta say i was happy to not see a list of codes spit out.

 

[General karthief]

Do you have a vacuum gauge?
Sound like your on the right path

 

[Cannon77550]

Do you have a vacuum gauge?
Sound like your on the right path

I do somewhere lol. I just moved half way across the country so im not sure if its at the house or in storage. What kinda vacuum should i be pulling if i can manage to find it?

 

[General karthief]

Close to 19 if I recall