High idle after throttle body install
Thread Starter
Melting Slicks
Joined: May 2007
Posts: 2,113
Likes: 0
From: Houston TX
High idle after throttle body install
I installed a polished ls1 throttle body a few days ago and ever since the install, I have had a high idle at start up. The idle sits at about 1100 n initial startup and stays there for around 15 seconds then drops back down into the 600 range.Anyone know what is causing this and how I can fix this?
Melting Slicks
Joined: May 2005
Posts: 3,394
Likes: 12
From: Leon Iowa
St. Jude Donor '06-'07-'08-'09
who ported it? They may of ported too far down in where the blade has to seal against the housing. I have seen this before. It's not so bad on the F body throttle bodys because they have an IAC to control the idle but on the vettes it's controled by the blade. If it's cut down at the blade too much it will do what you are describing.
Thread Starter
Melting Slicks
Joined: May 2007
Posts: 2,113
Likes: 0
From: Houston TX
Vengeance Racing did the polishing.They also didn't port it out around the blade area.When I initially asked for work to be done, they make sure I knew that there was not any actual porting done but just a polish and a port in front of the blade but not actually where the blade is touching the throttle body edges for the reasons you have described.
Former Vendor
Joined: Feb 2004
Posts: 10,876
Likes: 8
From: Las Vegas NV
St. Jude Donor '06 & '12
The problem you describe can also be linked to some sort of air leak. The leak would be in between the backside of the MAF and the manifold. Did you also verify the PCV was installed and sealed? Make sure your clamps are all tight, and there is no air gaps.
Thread Starter
Melting Slicks
Joined: May 2007
Posts: 2,113
Likes: 0
From: Houston TX
even if it was an air leak, why does it only hit 1100 only on start up but when I reach lights it stays around 600?
Le Mans Master
Joined: May 2005
Posts: 6,366
Likes: 249
From: Fort Lauderdale, Florida
There is a procedure outlined in the shop manual for an idle relearn, which you should try. It's different depending on whether you have an automatic or manual trans. I don't remember the entire procedure, but if you don't have the manual, maybe someone else will be able to direct you to where you may find the info. That will probably fix your problem.
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
This is common with a ported throttle body. As I understand it, when you turn the key the throttle blade closes and then opens to a fix angle that is set by the PCM. When you start, the PCM will then correct the idle speed. Now that you ported your TB, the fixed angle will allow in more air and therefore you initial startup RPM will increase. I have had several ported TB's, some have had this issue worse than others. Mark Shaner did one for me that was real bad and he took it back to provide to someone who had a monster cam and needed the extra air on startup. What he told me was mine had a lot of voids and to smooth it out he had to remove a little more than he normally does.
I think what you are seeing is normal with a ported TB based on my experience.
I think what you are seeing is normal with a ported TB based on my experience.
Team Owner
Joined: May 2006
Posts: 21,473
Likes: 356
From: Palmdale, Ca----- 2009 Cyber Gray 4LT A6 F55 452 RWHP 422 RWTQ- RIP 1998 C5 734 RWHP & 585 RWTQ-----
This is common with a ported throttle body. As I understand it, when you turn the key the throttle blade closes and then opens to a fix angle that is set by the PCM. When you start, the PCM will then correct the idle speed. Now that you ported your TB, the fixed angle will allow in more air and therefore you initial startup RPM will increase. I have had several ported TB's, some have had this issue worse than others. Mark Shaner did one for me that was real bad and he took it back to provide to someone who had a monster cam and needed the extra air on startup. What he told me was mine had a lot of voids and to smooth it out he had to remove a little more than he normally does.
I think what you are seeing is normal with a ported TB based on my experience.
I think what you are seeing is normal with a ported TB based on my experience.
there is a set AIR DEMAND for a stock TB and it will need to be adjusted at the PCM.
With the larger TB it still has the same demand for air so you will need your tuner or if you have HP Tuners you can reset the idle/start up air demand and this will give you a proper start up!
It's what I had to do! So you do not have an air leak anywhaere just a calibration adjustment!
Thanks,Matt
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Safety Car
Joined: Apr 2004
Posts: 3,932
Likes: 8
From: Hayward California
This is true but it can be adjusted!
there is a set AIR DEMAND for a stock TB and it will need to be adjusted at the PCM.
With the larger TB it still has the same demand for air so you will need your tuner or if you have HP Tuners you can reset the idle/start up air demand and this will give you a proper start up!
It's what I had to do! So you do not have an air leak anywhaere just a calibration adjustment!
Thanks,Matt
there is a set AIR DEMAND for a stock TB and it will need to be adjusted at the PCM.
With the larger TB it still has the same demand for air so you will need your tuner or if you have HP Tuners you can reset the idle/start up air demand and this will give you a proper start up!
It's what I had to do! So you do not have an air leak anywhaere just a calibration adjustment!
Thanks,Matt
time to do another planned mod so you could kill two birds with one stone and get it retuned.
