uracowman

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?

mvvette97

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.

uracowman

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.

0Jeff @ TPE

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.

uracowman

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?

striper

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.

vettenuts

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.

madmatt9471

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

uracowman

A battery disconnect/reconnect wouldn't fix this though would it?

AVB

time to do another planned mod so you could kill two birds with one stone and get it retuned.