Lt1 Idle issues - LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums

Welcome to LS1LT1.com/LS3forums.com - please click here to register...

LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums
Presented by:

New User? Register
LS1 Forums Register Photo Gallery Tech/FAQ Members List Calendar Auto Loans Search Today's Posts Mark Forums Read Auto EscrowInsurance
Premium Membership Videos Perf Tools Mobile/iPhone Link to Us! Social Groups Follow LS1LT1 on Twitter


Go Back   LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums > Engine Tech > LT1 | LT4 | L99 Engine Tech

LS1LT1.com is the premier Pontiac Forum on the internet. Registered Users do not see the above ads.
Reply
 
Share LinkBack Thread Tools
Old 06-28-2012, 09:36 PM   #1
Regular Member
 
Join Date: May 2009
Posts: 109
Keesling user's tech expertise is unknown at this point
Default Lt1 Idle issues

So my lt1 runs awesome lt4 cam ported heads 11:1 compression all the boltons

Except It does some funky things when idling. One stoplight its idling perfect at 850 and while going to the next stoplight

I would go to push in on the clutch and the car will actually idle higher like 1500+ until I come to a complete stop and then it will either go to about 1100 or it will idle at 500 almost dying.

Some times its perfect and there is not much correlation between hot or cold.

Except just now when I came out of the grocery store it wouldn't hold an idle at all and just died.

So I had to keep my foot on the gas to keep it up.

Iv'e replaced the iac adjusted the throttle screw and nothing works in that area as far as fixing the idle

I have a pcmforless tune and it runs great when your on the throttle but won't idle consistently. Not the tunes fault

There are no codes the iac works just fine (I can visually see the numbers change and lower the idle)

but sometimes the idle just shoots up or bogs its doesn't make sense.

No vacuum leaks. Maybe o2s? ICM?

What do you think? Help me lol
__________________
LT1, Hotcam, PRW 1.6, 11:1, Ported Heads, T56, 3:23, Pro5.0
Hooker shorties, y-pipe & cat-back, 52mm tb, custom CAI elec wp
xegr smog catx aluminum ds Lca's & relocation brackets Adj. panhard pcmforless tuned

Keesling is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Sponsored Links
Advertisement
 
Old 06-28-2012, 11:35 PM   #2
Regular Member
 
Join Date: Mar 2006
Posts: 130
IllusionalTA Apprentice Level Tech III
Default

How is idle not tunes fault? Worse case bump idle with set screw in order to Get by, but get to a competent tuner
Quote:
Originally Posted by Keesling View Post
So my lt1 runs awesome lt4 cam ported heads 11:1 compression all the boltons

Except It does some funky things when idling. One stoplight its idling perfect at 850 and while going to the next stoplight

I would go to push in on the clutch and the car will actually idle higher like 1500+ until I come to a complete stop and then it will either go to about 1100 or it will idle at 500 almost dying.

Some times its perfect and there is not much correlation between hot or cold.

Except just now when I came out of the grocery store it wouldn't hold an idle at all and just died.

So I had to keep my foot on the gas to keep it up.

Iv'e replaced the iac adjusted the throttle screw and nothing works in that area as far as fixing the idle

I have a pcmforless tune and it runs great when your on the throttle but won't idle consistently. Not the tunes fault

There are no codes the iac works just fine (I can visually see the numbers change and lower the idle)

but sometimes the idle just shoots up or bogs its doesn't make sense.

No vacuum leaks. Maybe o2s? ICM?

What do you think? Help me lol
IllusionalTA is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 06-29-2012, 06:25 AM   #3
Global Moderator
 
cocobolo95's Avatar
 
Join Date: Sep 2008
Location: Fruitland Park,Florida
Posts: 9,485
cocobolo95 Tradesman Level Tech II
Default

Did you base your assumption of no codes on a code scan, or because the ses light isn't on. If based on ses light not on then you need to scan for codes. Not all codes light the ses. Since you think the tune is good, did car idle well when tune was installed, then idle went bad? Or did it idle bad from the get go after tune was installed?
cocobolo95 is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 06-29-2012, 10:44 AM   #4
Regular Member
 
Join Date: May 2009
Posts: 109
Keesling user's tech expertise is unknown at this point
Default

Since when was pcmforless incompetent ?
I have a snapon ethos and there are no codes for this idling issue
It wouldn't hold an idle with my bolt on tune so I had it retuned for the cam and whatnot and it was fine for awhile and now it is acting up
The tuner sure thinks it isn't the tune and told me to adjust the idle screw and reset the iac. So I did. It doesn't matter where the idle screw is it will either idle way too high or will bog down and idle way too low but sometimes it will idle fine
__________________
LT1, Hotcam, PRW 1.6, 11:1, Ported Heads, T56, 3:23, Pro5.0
Hooker shorties, y-pipe & cat-back, 52mm tb, custom CAI elec wp
xegr smog catx aluminum ds Lca's & relocation brackets Adj. panhard pcmforless tuned

Keesling is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 06-29-2012, 10:49 AM   #5
Regular Member
 
Mystery Bird's Avatar
 
Join Date: Apr 2010
Location: Western MA
Posts: 4,126
Mystery Bird Apprentice Level Tech II
Default

I didn't see what year your car is, can you use Datamaster or Freescan to see what it's doing under those conditions?
__________________
http://www.youtube.com/user/MysteryBird1?feature=watch
1995 TA: Converted Nose...381 LT1...4L80E...12 bolt...3.90 Gears...4000 TC
Best 1/4 so far 10.87@ 123, 1.48 60ft, 3450lbs.
Mystery Bird is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 06-29-2012, 02:40 PM   #6
Regular Member
 
Join Date: May 2009
Posts: 109
Keesling user's tech expertise is unknown at this point
Default

Its a 92 But the lt1 is a 96 So its obd2. I have an ethos. Its a scantool. It can graph and show just about anything I can think of.
What should I be looking for? I can see everything with it and all looks to be normal but iv'e driven around and looked at it so much my head throbs
tps is .69 with the iac counts at around 48 usually Before i put a new iac in it would get stuck at 100 or 0 and with the new one that problem seems to have gone away.
But it doesn't seem to be able to compensate for the idle fluctuations.
Maybe an o2? One of them is on the lazy side and my right bank fuel trim is quite different than the left. One is at 3 or 4 and the other is pulling a little
I think its long term that is a bit far off but when on the throttle they even out.
Idk I didn't have this problem before I ported the heads and did the cam
__________________
LT1, Hotcam, PRW 1.6, 11:1, Ported Heads, T56, 3:23, Pro5.0
Hooker shorties, y-pipe & cat-back, 52mm tb, custom CAI elec wp
xegr smog catx aluminum ds Lca's & relocation brackets Adj. panhard pcmforless tuned

Keesling is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 06-30-2012, 10:06 PM   #7
Regular Member
 
Join Date: Jul 2010
Posts: 37
idoxlr8 user's tech expertise is unknown at this point
Default

FWIW TPS volts should be .67 at idle with throttle blade closed. Bryan told me the same thing about opening the throttle blade. Thing is you have to adjust the TPS to maintain the .67 volts. You can slot the screw holes to allow you to turn the TPS and get the correct voltage with the throttle blade cracked a bit.

I am dealing with the same issue on my 96 LT1-383. Same deal it was fine and now with hot weather it wants to drop idle down to 300rpms or so and die when ever I come to a stop.
idoxlr8 is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 07-01-2012, 08:57 PM   #8
Regular Member
 
Join Date: May 2009
Posts: 109
Keesling user's tech expertise is unknown at this point
Default

Meh .02 volts isn't going to hurt anything. Besides its only that high because I currently have the throttle blades open too much
because otherwise it will die instead of idling at 500 when it does mess up. Just to make it driveable at the moment instead of wearing my battery down when it dies.
The way I have my tps I can close the throttle blades completely and get .62 volts.
Before I did the cam and tune I had the same tb and the voltage was at .78 with no ill effects. never an idle issue before the cam...
__________________
LT1, Hotcam, PRW 1.6, 11:1, Ported Heads, T56, 3:23, Pro5.0
Hooker shorties, y-pipe & cat-back, 52mm tb, custom CAI elec wp
xegr smog catx aluminum ds Lca's & relocation brackets Adj. panhard pcmforless tuned

Keesling is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 07-06-2012, 08:07 AM   #9
Regular Member
 
Join Date: May 2009
Posts: 109
Keesling user's tech expertise is unknown at this point
Default

Any ideas?
__________________
LT1, Hotcam, PRW 1.6, 11:1, Ported Heads, T56, 3:23, Pro5.0
Hooker shorties, y-pipe & cat-back, 52mm tb, custom CAI elec wp
xegr smog catx aluminum ds Lca's & relocation brackets Adj. panhard pcmforless tuned

Keesling is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 07-27-2012, 02:56 PM   #10
Regular Member
 
Join Date: May 2009
Posts: 109
Keesling user's tech expertise is unknown at this point
Default

Going to fix a small leak I found and adjust the stop screw to change the tps back to .67. Will report back
__________________
LT1, Hotcam, PRW 1.6, 11:1, Ported Heads, T56, 3:23, Pro5.0
Hooker shorties, y-pipe & cat-back, 52mm tb, custom CAI elec wp
xegr smog catx aluminum ds Lca's & relocation brackets Adj. panhard pcmforless tuned

Keesling is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 07-27-2012, 07:18 PM   #11
Regular Member
 
Join Date: Mar 2008
Location: Atlanta, GA
Posts: 1,229
bobdec Apprentice Level Tech II
Default

Two things to get idle correct. TPS voltage s/b .45-.75 volts AND your Idle Air Counts (IAC) should be around 20-40. The IAC count at 20-40 means the PCM is controlling idle speed, not the TB stop screw. If you can't get IAC AND voltage correct then you may have to slot the mounting holes in the TPS so you can get the correct voltage with the blades slightly cracked open enough to allow IAC to keep idle smooth. Bottom line adjust blade stop till IAC is correct, then if voltage is out of spec slot the TPS holes to get voltage in spec at correct IAC counts. Your balancing TB air flow and IAC air flow, since the IAC air goes through the intake plenums to reach each cylinder Vs the TB only letting air into the front, it's critical to have correct IAC valve operation for smooth idle, no split trims, and transition to higher RPM.
__________________
I'm Bob.. 1994 Z28, A4, Stall, CAI, Cam, RR's, 342 rear, LT's , CatBack, Tuned

Last edited by bobdec; 07-27-2012 at 07:21 PM.
bobdec is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 07-28-2012, 03:10 AM   #12
Regular Member
 
Join Date: May 2009
Posts: 109
Keesling user's tech expertise is unknown at this point
Default

Quote:
Originally Posted by bobdec View Post
Two things to get idle correct. TPS voltage s/b .45-.75 volts AND your Idle Air Counts (IAC) should be around 20-40. The IAC count at 20-40 means the PCM is controlling idle speed, not the TB stop screw. If you can't get IAC AND voltage correct then you may have to slot the mounting holes in the TPS so you can get the correct voltage with the blades slightly cracked open enough to allow IAC to keep idle smooth. Bottom line adjust blade stop till IAC is correct, then if voltage is out of spec slot the TPS holes to get voltage in spec at correct IAC counts. Your balancing TB air flow and IAC air flow, since the IAC air goes through the intake plenums to reach each cylinder Vs the TB only letting air into the front, it's critical to have correct IAC valve operation for smooth idle, no split trims, and transition to higher RPM.
Good info, I already did all that. The problem was that unless the stop screw was adjusted out all the way holding the throttle open it would die, Ended up being a bad iacm. Replaced that and it was intermittent and would idle properly until you backed out and stopped at which point it wouldn't idle down or it would idle down too much.
I tinkered with the stop screw and the tps voltage with its running and my scantool in the enginebay making sure the tps was within range and the iac was between 20-50 and all was well but the engine rpm's were out of whack still and it takes forever to idle down.
Today I drove it around a bit and took about two turns off the idle screw to get the idle down after fixing the leak I found ( could have been intermittent)
It idled down to around 1000 on my tach (probably 950) and ran fine.
Until I backed out of the driveway and it started idling up.
Pulled back up and popped the hood. On a whim I wiggled the wires that go to the tps and what do you know the thing idled perfectly after that.
Going to fix that tomorrow and it should be about perfect except it still seems to take forever to idle down from 1500 takes about 2 seconds after I fully stop for it to idle down from there, And while rolling its alway at 1500.
Which is fine with me but doesn't seem normal.
Anyway I guess it was a combination of a bad IAC motor and a small intermittent vac leak and a bad wire on my tps sensor. ( which for some reason never showed up as a bad reading on the scanner)

I'm sure it will have a new set of issues tomorrow
__________________
LT1, Hotcam, PRW 1.6, 11:1, Ported Heads, T56, 3:23, Pro5.0
Hooker shorties, y-pipe & cat-back, 52mm tb, custom CAI elec wp
xegr smog catx aluminum ds Lca's & relocation brackets Adj. panhard pcmforless tuned

Keesling is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 07-28-2012, 09:25 AM   #13
Regular Member
 
Join Date: Mar 2008
Location: Atlanta, GA
Posts: 1,229
bobdec Apprentice Level Tech II
Default

Are you sure the IAC air port on the TB is aligned with the idle air plenum in the intake. And there are no runners in the TB that will allow IAC air to enter the TB main openings (blades). Some aftermarket TB's were designed for TBI 5.7's not the TPI LT1's, just a wild thought. By the way a second or two for IAC to adjust idle is normal, IAC it's not that fast on purpose in order to prevent a fluttering idle. Your RPM's are way out and PCM does not step IAC that quick. Usually RPM differences are smaller and the PCM uses timing retard or advance to quickly adjust idle (idle overspeed and underspeed timing tables), and then IAC more gradually to get it correct. At startup (ignition on) the PCM sets IAC to a 'park position', around 65 counts (it's programable) to allow more air and get the plunger about midway till it kicks over, then after kickover the PCM moves it to obtain desired idle speed.
Scanner should show your TPS wire problem, key on / engine off wiggle the wire, either a scanner or a voltmeter should show something. One wire is ground, one +5 volts and the other is signal to PCM s/b TPS closed voltage of .45-.75 and should increase smoothly to 4.5 volts w/o any jerks or sudden jumps or drops as throttle blades are advanced to full open.
__________________
I'm Bob.. 1994 Z28, A4, Stall, CAI, Cam, RR's, 342 rear, LT's , CatBack, Tuned

Last edited by bobdec; 07-28-2012 at 09:34 AM.
bobdec is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 07-28-2012, 02:23 PM   #14
Regular Member
 
Join Date: May 2009
Posts: 109
Keesling user's tech expertise is unknown at this point
Default

Quote:
Originally Posted by bobdec View Post
Are you sure the IAC air port on the TB is aligned with the idle air plenum in the intake. And there are no runners in the TB that will allow IAC air to enter the TB main openings (blades). Some aftermarket TB's were designed for TBI 5.7's not the TPI LT1's, just a wild thought. By the way a second or two for IAC to adjust idle is normal, IAC it's not that fast on purpose in order to prevent a fluttering idle. Your RPM's are way out and PCM does not step IAC that quick. Usually RPM differences are smaller and the PCM uses timing retard or advance to quickly adjust idle (idle overspeed and underspeed timing tables), and then IAC more gradually to get it correct. At startup (ignition on) the PCM sets IAC to a 'park position', around 65 counts (it's programable) to allow more air and get the plunger about midway till it kicks over, then after kickover the PCM moves it to obtain desired idle speed.
Scanner should show your TPS wire problem, key on / engine off wiggle the wire, either a scanner or a voltmeter should show something. One wire is ground, one +5 volts and the other is signal to PCM s/b TPS closed voltage of .45-.75 and should increase smoothly to 4.5 volts w/o any jerks or sudden jumps or drops as throttle blades are advanced to full open.
It's aligned. Before I put a cam in it and ported the heads I didn't have these problems. Same throttle body.
Does the same apply with the park position if it's a manual?
My scanner is MIA right now at my fathers house but I know wiggling it will change something with the scanner hooked up just odd that it didn't show up when hitting the bump leaving my driveway which seems to trigger the idle issue.
I used to have tbi in this car and the throttle body wouldn't even be possible to bolt up. Do you mean the tpi and lt1 t/b's are different where the iac passage is?
Either way it's right As it worked before flawlessly till demanding more air at idle. Thanks for the help though
__________________
LT1, Hotcam, PRW 1.6, 11:1, Ported Heads, T56, 3:23, Pro5.0
Hooker shorties, y-pipe & cat-back, 52mm tb, custom CAI elec wp
xegr smog catx aluminum ds Lca's & relocation brackets Adj. panhard pcmforless tuned

Keesling is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 07-28-2012, 03:18 PM   #15
Global Moderator
 
cocobolo95's Avatar
 
Join Date: Sep 2008
Location: Fruitland Park,Florida
Posts: 9,485
cocobolo95 Tradesman Level Tech II
Default

What Bob meant by park position is where pcm commands iac when car starts. The other tb he was talking about was used on tuned port injection on 3rd gens from 86-92. The tb used was different than lt1 tb. And some aftermarket tb's are made to L98 specs rather than LT1.
cocobolo95 is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Sponsored Links
Advertisement
 
Reply

Bookmarks

Thread Tools

Posting Rules
You may not post new threads
You may not 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


» Recommended
Find technical articles on a Chevy Corvette, including tips and tricks on a Chevy Camaro and expert advice for Pontiac Firebird, along with reviews on the Cadillac CTS.
» Auto Insurance
» Sponsors
Powered by vBadvanced CMPS v3.2.2

All times are GMT -5. The time now is 06:14 PM.



Powered by vBulletin® Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.5.2
Copyright © 2005 - 2011 by LS1LT1.com

Our Friends:


Illegal Street Racing | Super Cars | LT1 Tech Articles