What does it mean when I unplug a vacuum line and my idle doesn't change? - Ford Mustang Forums : Corral.net Mustang Forum
Go Back   Ford Mustang Forums : Corral.net Mustang Forum > Modular Tech Forums > GT & SOHC

Corral.net is the premier Ford Mustang Forum on the internet. Registered Users do not see the above ads.
Reply
 
LinkBack Thread Tools Display Modes
Old 07-16-2009, 05:28 PM   #1
Registered User

Trader Feedback: (2)
 
Join Date: Mar 2005
Location: Indy
Posts: 318

What does it mean when I unplug a vacuum line and my idle doesn't change?

I'm having a small surge/gurgle in my idle which is annoying me to no end. My car has also decided that when I push in the clutch at anything over 2500 RPMs it goes full lean and the RPMs plunge, sometimes to only a few hundred, before it rights itself. This makes for rough driving and me having a mild heart-attack each time I see them plunge.

So, I have been reading and thought maybe the EGR was stuck open. When I unplugged the vacuum hose on top of it (to see what would happen), nothing changed about the car. There was some vacuum in the hose, but the idle note, RPMs and mixture didn't change.

So, I went to my throttle body and unplugged the driver's side vacuum hose. Again, nothing changed. There was a weak vacuum in the hose.

Then, I unplugged the throttle-body's passenger's side vacuum connection and the idle stumbled more and my mixture went lean (about 16.5-17).

I have a few questions:

1. If unplugging the driver's side vacuum hose did not affect the idle or anything about the engine, does that signify a vacuum leak? Or is that side on a different "path" and has no effect on the engine?

2. At idle my vacuum is about 22" (as measured by my boost/vac gauge, connected to the driver's side vacuum connection). When I disconnected the line leading to the throttle body, the vacuum dropped to 18". Is that normal? Also, would it be possible to have a vacuum leak and still pull this much vacuum at idle?

3. During this whole time of unplugging the EGR and all the vacuum lines going to my throttle body, I never once set off a check-engine light. What's up with that?

4. When I clutch in (especially after driving on the highway) the RPMs plummet to idle, sometimes even a few hundred RPMs below idle, before they catch themselves. It hasn't stalled yet, but my idle is raised 150 RPMs above stock so had it been stock it may have stalled. Does this sound like an EGR problem? A vacuum issue? Something else?

Thanks!
__________________
2001 Laser Red GT
Vortech V3-Si with 42lb Injectors (Tuned with Sniper SF)
Pro 5.0 Shifter, Flowmaster Super-40 Exhaust, Offroad H-Pipe
AirBrontosaurus is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Sponsored Links
Advertisement
 
Old 07-16-2009, 05:46 PM   #2
Registered User
 
04Ryan's Avatar

Trader Feedback: (8)
 
Join Date: May 2009
Location: Palm Bay, FL
Posts: 2,284

The EGR only gets a vacuum signal when the EEC wants it to open...and that is usually only during cruising conditions. Thats why it didn't change or even trip a CEL...had you left it unhooked and drove the car around for several miles it would have. But sounds like it's not a vacuum leak...its really hard to pull 22" of vacuum with a leak of any size. As you proved by unhooking the one line and the vacuum rose to 18"...any chance you can get a video clip of it making this noise? As far as the rpm's dropping you might want to look into the idle air motor...from what I've been hearing around here they are a problem area. They need cleaned out regualry...hope that helps!
__________________
04' Anniv. Ed GT
Eaton Powered 2V
10.34@133 1.45 60'
Sold And Gone
04Ryan is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote Quick reply to this message
Old 07-16-2009, 06:00 PM   #3
Registered User

Trader Feedback: (2)
 
Join Date: Mar 2005
Location: Indy
Posts: 318

Thanks 04Ryan!

Unfortunately I just replaced my IAC and it didn't make a bit of difference.

I agree that 22" of vacuum seems like I don't have anything major. I was just hoping someone would say "Oh, it doesn't change idle when you disconnect that hose? Classic symptom of your blah-blah-blah going bad, buy a new one and you'll be fine!"

As far as a video, I actually don't have a video camera or anything. I'll look around and see what I can do.

Again, thanks for the reply!
__________________
2001 Laser Red GT
Vortech V3-Si with 42lb Injectors (Tuned with Sniper SF)
Pro 5.0 Shifter, Flowmaster Super-40 Exhaust, Offroad H-Pipe
AirBrontosaurus is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote Quick reply to this message
Old 07-16-2009, 07:33 PM   #4
Registered User
 
04Ryan's Avatar

Trader Feedback: (8)
 
Join Date: May 2009
Location: Palm Bay, FL
Posts: 2,284

How bout a digital camera? Most these days will take video with sound that will be good enough for what we need. Yea I know how ya feel...hoping that it's something simple but with my luck it hardly ever is. As far as the idle I was browsing the SVT forum on here and the 03/04 cobra guys seem to have the same thing but it's much more common on their cars. Do a search on the cobra stuff and see if you can come up with anything...most of them got it fixed just by putting a tune on their car. Maybe you might need to clear the memory on your computer and start fresh.
__________________
04' Anniv. Ed GT
Eaton Powered 2V
10.34@133 1.45 60'
Sold And Gone
04Ryan is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote Quick reply to this message
Old 07-16-2009, 11:24 PM   #5
Registered User

Trader Feedback: (2)
 
Join Date: Mar 2005
Location: Indy
Posts: 318

IDEA! (for the deceleration issue)

Would a malfunctioning bypass valve cause my ultra-lean and ultra-fast deceleration? And could it affect my idle?

If the BPV is stuck closed, then when I let off the gas the supercharger will still force air into the engine, causing it to go super lean and nearly die... UNTIL the blower stops spinning and the car can get back to idle.

Is that something that's possible? Would a bypass valve that isn't getting vacuum cause these problems?
__________________
2001 Laser Red GT
Vortech V3-Si with 42lb Injectors (Tuned with Sniper SF)
Pro 5.0 Shifter, Flowmaster Super-40 Exhaust, Offroad H-Pipe
AirBrontosaurus is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote Quick reply to this message
Old 07-17-2009, 01:19 AM   #6
Registered User
 
04Ryan's Avatar

Trader Feedback: (8)
 
Join Date: May 2009
Location: Palm Bay, FL
Posts: 2,284

I doubt it...only because I drove around with my bypass unhooked just to see what it would do and it didn't run differently at all. But it's always something to check...never rule anything out untill you've looked over it and verified it's working properly. Hope you get it figured out soon!
__________________
04' Anniv. Ed GT
Eaton Powered 2V
10.34@133 1.45 60'
Sold And Gone
04Ryan is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote Quick reply to this message
Old 07-17-2009, 01:45 AM   #7
Registered User
 
Josh97Stang's Avatar

Trader Feedback: (0)
 
Join Date: Jul 2009
Location: Bowling Green Ky
Posts: 75

my moms cars bypass valve went out and it had a hard time at idle and some times it would allmost stall at stop signs when u started to hit the gas
Josh97Stang is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Reply

Bookmarks

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Ford Mustang Forums : Corral.net Mustang Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools
Display Modes

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -4. The time now is 01:25 PM.



Powered by vBulletin® Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Friendly URLs by vBSEO 3.5.2
© 2010-2011 Corral.net

Garage Plus vBulletin Plugins by Drive Thru Online, Inc.