Hanging idle and booster vac issue
Thread Starter
Teching In
Joined: Jun 2015
Posts: 27
Likes: 4
Hanging idle and booster vac issue Hey all!
Have a 6L boosted fox and recently became stumped hoping someone has gone through the same issue. After getting on it, the car would hang at the rpm that it was left at. Cruising in the highway was like cruise control. Couldn't get it to idle down. If you start it in P OR N the idle starts off at 18-2000rpm (supposed to be high 800) and if you rev it it will stay at where it went to highest not coming down. Now my IAC is showing good on my Holley digital dash, throttle is DBC and is working properly showing throttle position properly as it should.
The vacuum setup is all new hoses and they are all connected perfectly still. The red flag is my vac hose from the brake booster to the vac block collapses with vacuum. (Can try swap out vac hose for fuel hose but shouldn't need to) The inline valve is the proper way and works when it's out and blow through it. It's the only hose that collapses. Took it off and plugged the vac block where it goes and still nothing changes.... only after a good 18ish pound hit of boost this appeared.
Anyone have ideas. I'm lost as I've basically built this entire deal myself and have run out of ideas. Brake booster faliure with being hit with boost?
Have a 6L boosted fox and recently became stumped hoping someone has gone through the same issue. After getting on it, the car would hang at the rpm that it was left at. Cruising in the highway was like cruise control. Couldn't get it to idle down. If you start it in P OR N the idle starts off at 18-2000rpm (supposed to be high 800) and if you rev it it will stay at where it went to highest not coming down. Now my IAC is showing good on my Holley digital dash, throttle is DBC and is working properly showing throttle position properly as it should.
The vacuum setup is all new hoses and they are all connected perfectly still. The red flag is my vac hose from the brake booster to the vac block collapses with vacuum. (Can try swap out vac hose for fuel hose but shouldn't need to) The inline valve is the proper way and works when it's out and blow through it. It's the only hose that collapses. Took it off and plugged the vac block where it goes and still nothing changes.... only after a good 18ish pound hit of boost this appeared.
Anyone have ideas. I'm lost as I've basically built this entire deal myself and have run out of ideas. Brake booster faliure with being hit with boost?
9 Second Club
Joined: Nov 2003
Posts: 13,616
Likes: 185
From: Norn Iron
It's called tuning. It's clearly tuned/setup badly.
Either throttle open too much, and/or idle valve badly tuned.
If a vac hose is collapsing..clearly that hose is not suitable for vacuum. So use proper hose.
You're going to either need to provide better info on parts or images, as clearly there are multiple issues here.
Either throttle open too much, and/or idle valve badly tuned.
If a vac hose is collapsing..clearly that hose is not suitable for vacuum. So use proper hose.
You're going to either need to provide better info on parts or images, as clearly there are multiple issues here.
Thread Starter
Teching In
Joined: Jun 2015
Posts: 27
Likes: 4
It's called tuning. It's clearly tuned/setup badly.
Either throttle open too much, and/or idle valve badly tuned.
If a vac hose is collapsing..clearly that hose is not suitable for vacuum. So use proper hose.
You're going to either need to provide better info on parts or images, as clearly there are multiple issues here.
Either throttle open too much, and/or idle valve badly tuned.
If a vac hose is collapsing..clearly that hose is not suitable for vacuum. So use proper hose.
You're going to either need to provide better info on parts or images, as clearly there are multiple issues here.
9 Second Club
Joined: Nov 2003
Posts: 13,616
Likes: 185
From: Norn Iron
if it was built and tuned correctly, there would be no problems.
And it's a little stupid to say a hose is collapsing but is suitable for vacuum....well if it was suitable, it wouldnt be collapsing.
Yes there is another issue....whoever is building and tuning it. What did the tuner say when he was tuning it and these problems were apparent ? Did he not have a look at things ?
And boost is irrelevant...because you arent stating any problems under boost.
And it's a little stupid to say a hose is collapsing but is suitable for vacuum....well if it was suitable, it wouldnt be collapsing.
Yes there is another issue....whoever is building and tuning it. What did the tuner say when he was tuning it and these problems were apparent ? Did he not have a look at things ?
And boost is irrelevant...because you arent stating any problems under boost.
Thread Starter
Teching In
Joined: Jun 2015
Posts: 27
Likes: 4
if it was built and tuned correctly, there would be no problems.
And it's a little stupid to say a hose is collapsing but is suitable for vacuum....well if it was suitable, it wouldnt be collapsing.
Yes there is another issue....whoever is building and tuning it. What did the tuner say when he was tuning it and these problems were apparent ? Did he not have a look at things ?
And boost is irrelevant...because you arent stating any problems under boost.
And it's a little stupid to say a hose is collapsing but is suitable for vacuum....well if it was suitable, it wouldnt be collapsing.
Yes there is another issue....whoever is building and tuning it. What did the tuner say when he was tuning it and these problems were apparent ? Did he not have a look at things ?
And boost is irrelevant...because you arent stating any problems under boost.
If your booster hose is collapsing, as said, you need a better hose. Are you using a Holley
ECU, what does the IAC position show when high idle. You could have a bad IAC valve, or
a vac leak. Does the CL comp. show a big correction. A large leak will make the computer
add more fuel, thinking you opened the throttle, and if the IAC is out of range, it cant control it.
ECU, what does the IAC position show when high idle. You could have a bad IAC valve, or
a vac leak. Does the CL comp. show a big correction. A large leak will make the computer
add more fuel, thinking you opened the throttle, and if the IAC is out of range, it cant control it.
Thread Starter
Teching In
Joined: Jun 2015
Posts: 27
Likes: 4
If your booster hose is collapsing, as said, you need a better hose. Are you using a Holley
ECU, what does the IAC position show when high idle. You could have a bad IAC valve, or
a vac leak. Does the CL comp. show a big correction. A large leak will make the computer
add more fuel, thinking you opened the throttle, and if the IAC is out of range, it cant control it.
ECU, what does the IAC position show when high idle. You could have a bad IAC valve, or
a vac leak. Does the CL comp. show a big correction. A large leak will make the computer
add more fuel, thinking you opened the throttle, and if the IAC is out of range, it cant control it.
Trending Topics
What is the IAC % when this happens? What is the IAC % at hot idle? What's the IAC hold value? What's the RPM above idle to enable idle control?
Andrew
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo 9 Second Club
Joined: Nov 2003
Posts: 13,616
Likes: 185
From: Norn Iron
Sadly trying to diagnose stuff like this remotely, when you cannot get proper answers and the person asking isnt willing to listen etc, is incredibly difficult.
Thread Starter
Teching In
Joined: Jun 2015
Posts: 27
Likes: 4
You bet! So whatnot was doing is always dropping to 0. When I'd rev to 2k let's say it would raise to 15.. and hold.. raise rpm to 3k and it would raise to 40 and hold idle. I changed out the IAC and now what's happened is Holley has self learned my incorrect setup and the tune is now off. I am getting my original tune sent to me to load tonight. There was a few issues I dealt with but should be sorted of I can get the tune loaded back to what it was. Self learning is good till there's an issue I guess. Kinda tough when you ask a question and people jump on you though. This is a brand new project. I built it over 3 years and learned as I went. It has been challenging but what I learned most is that the car community has a lot of support and information and there is always the few who belittle you for not knowing what you don't know. Future guys, remember that what you know others don't. I'm proud to say I took a car and swapped an engine and built a turbo kit and fabricated everything myself to what I consider a show car now. Thanks for your help some, to others... Remember you were learning once too.
9 Second Club
Joined: Nov 2003
Posts: 13,616
Likes: 185
From: Norn Iron
Everyone is learning...but they need to listen to advice in order to be able to learn, even if it isnt what you want to hear.
That's a huge problem with the internet, people ask questions, but when they dont get the answers they want...they go in a huff. But they will very likely be the answers they need.
That's a huge problem with the internet, people ask questions, but when they dont get the answers they want...they go in a huff. But they will very likely be the answers they need.
When you get the tune sent to you, make a copy so you can always have it
to reload. You might turn off the learn while you shoot the trouble. Is it DBW or
cable. Make sure you do a TPS autoset.
Never mind, I forgot it had an IAC.
Guessing it orig ran OK-did you by chance ever weld on it with the ECU in the car?
I did and it hurt the tune, you have to pull all the harness's. What RPM does the
closed loop and learn start at. If you do simple things like even changing vac hoses
around, and its not in CL, it can affect things, engine sees more/less air, idles in
a diff cell.
to reload. You might turn off the learn while you shoot the trouble. Is it DBW or
cable. Make sure you do a TPS autoset.
Never mind, I forgot it had an IAC.
Guessing it orig ran OK-did you by chance ever weld on it with the ECU in the car?
I did and it hurt the tune, you have to pull all the harness's. What RPM does the
closed loop and learn start at. If you do simple things like even changing vac hoses
around, and its not in CL, it can affect things, engine sees more/less air, idles in
a diff cell.
Last edited by forcd ind; Jul 16, 2019 at 06:27 AM.
You bet! So whatnot was doing is always dropping to 0. When I'd rev to 2k let's say it would raise to 15.. and hold.. raise rpm to 3k and it would raise to 40 and hold idle. I changed out the IAC and now what's happened is Holley has self learned my incorrect setup and the tune is now off. I am getting my original tune sent to me to load tonight. There was a few issues I dealt with but should be sorted of I can get the tune loaded back to what it was. Self learning is good till there's an issue I guess. Kinda tough when you ask a question and people jump on you though. This is a brand new project. I built it over 3 years and learned as I went. It has been challenging but what I learned most is that the car community has a lot of support and information and there is always the few who belittle you for not knowing what you don't know. Future guys, remember that what you know others don't. I'm proud to say I took a car and swapped an engine and built a turbo kit and fabricated everything myself to what I consider a show car now. Thanks for your help some, to others... Remember you were learning once too.
Bottom line, you have a vacuum leak somewhere.
Andrew
Thread Starter
Teching In
Joined: Jun 2015
Posts: 27
Likes: 4
If it was fine before and now IAC is deteriorating to zero at idle, that indicates a vacuum leak. When you rev it up, the IAC moves to its Hold position, which to me seems like is set to 40 (common setting). but because there is a vacuum leak, when IAC closes, RMP can't drop low enough to enable idle control, blah...blah..blah...
Bottom line, you have a vacuum leak somewhere.
Andrew
Bottom line, you have a vacuum leak somewhere.
Andrew
A vacuum leak can also be identified very easily if you know and understand your Holley tune. For instance, I have a Dominator on my 67 Cougar. I know from working with it and tuning it that the normal (everything working properly) it idles at 43-44kPa. If there was a sudden vacuum leak it would immediately start to idle at a higher kPa because the vacuum signal will deteriorate and the MAP sensor will read that as the engine pulling less vacuum.
Andrew
Andrew