Vaccumm leak and running poorly

[3spd on floor]

Hey, yesterday when i started up my 94 it turned over but didnt catch for a second, and then when it restarted i heard a hissing like a vaccumm leak. its running, but has a really rough idle and will die if left in gear without giving it a little gas. then once it warms up it idles very fast (1500rpm) and wont drop. check engine light does come on.

now i know that basically i'm going to have to just sit and stare under the hood for a few hours til i find the hose that pulled loose, done it a few times before.

anyone have any ideas what to check first? its cold and rainy and dark and i'd like to get it fixed pretty quickly.

 

[J. Danna]

My '94 would do that. A rubber cap that seals off an unused port on the vacuum manifold (which is on the driver's side near the fire wall) would pop off when I started the engine. I think it just got old and loose. You can buy replacement rubber caps at any auto parts store. If it isn't that, I suggest starting at the manifold looking for disconnected hoses there, and then following each hose from the manifold to the other end of the hose. Good luck!

 

[atl95gt]

this sounds like my problem - i found a rubber cap sitting on a fuel rail this afternoon after my 5.0L started idling rough and what sounded like a vacuum leak. i cant find where the end cap goes. i have spent the last three hours looking for the vacuum leak with no luck

i need help - where could this end cap go? you said that "rubber cap that seals off an unused port on the vacuum manifold (which is on the driver's side near the fire wall)" but where?

 

[J. Danna]

The manifold is not very big. On my '94, it is on the side of the intake manifold and below the windshield wiper motor. If you follow the large vacuum hose from the brake booster, it will lead you to the manifold. I'm not sure about the '97.

 

[atl95gt]

i found it - in case anyone has a similar issue - under the fuel rails on the driver side manifold is a tube that must be capped off. thanks to J. Danna for his help.

 

[J. Danna]

Glad you found it atl95gt. These kinds of things can drive you nuts!

 

[3spd on floor]

well i got lucky and it only took me about 2 minutes to find the loose hose. theres a big distribution block thingy that gets vaccum from the manifold, and one of the hoses pulled off it.

THANKS!

 

[monkeydude3]

I still think I have some kind of funky vacuum leak..... it idles fast when it's all warmed up!!! I have a 1994 XL 4.0L OHV 5 speed manual... oh well.... I hate vacuum leaks....