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Stupid idle question

4K views 23 replies 5 participants last post by  99Pewterz286Rag 
#1 · (Edited)
Hey guys, so as odd as this may seem, I want to lower my idle. I love the sound of a lopey idle, so K figured why not see if I can take it down over a weekend. Currently, it sits around 1000 when warmed up. It is an LT4 heads, intake, and I am assuming cam, so is it wrong to assume it can handle around 600 rpm at idle, maybe even 500?

And if it can, how would I go about getting it there? I doubt that it's as easy as tightening up the set screw, but I'd love a place to start because this could hopefully be a free/cheap mod that I can knock out over a lazy Sunday.
 
#3 · (Edited by Moderator)
Is there any way to get into the pcm without tunercat or a dyno tuner? I'm sorry if I sound uneducated but I'm trying to remedy that!

You can send your lt1 94-97 pcm to www.lt1pcmtuning.com

You will fill out any changes made to engine/trans/rear end ratio. And different tire sizes, coolant fan turn on temps. Also he can tune vats security out of pcm, if you wish.

For 93 model ecm with removable prom module, you would only have to send him the blue prom module for any changes made.
 
#6 ·
Head & cam builds generally have a "command" idle programmed around 800-850 RPM so they do idle decent

1000 sounds high. A common cause of hgt idle is a vacuum leak so confirm you don't have one

The stop screw on TB should really never be messed with. Some people do adjust it on aftermarket TB attempting them to idle better. This will throw off the TPS and negatively affect line pressure for automatic cars

Your mods done by P.O. can be hard to chase wtf may be going on

Having a scan tool is helpful in reading exactly what is going on. TPS VDC and IAC counts being 2 things
 
#8 ·
The set screw is simply a stop to keep the butterflies from sticking in their bores when snapped closed. If you try to adjust the idle speed with it, the PCM will just compensate for it with the IAC. It really won't affect the line pressure of the transmission, but it will screw with the IAC counts and BLM's at idle.

Preferred idle speed will depend upon the cam specs. Most of the smallish cams that guys are using on here idle happily at 800-900 rpm. My GM847 cam is set to idle at 1000, and my circle track engines all idled at around 1800, so it just depends upon the cam grind.
 
#10 ·
The set screw is simply a stop to keep the butterflies from sticking in their bores when snapped closed. If you try to adjust the idle speed with it, the PCM will just compensate for it with the IAC. It really won't affect the line pressure of the transmission, but it will screw with the IAC counts and BLM's at idle.

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actually fing with the stop screw will affect line pressure in tranny (automatic). opening up the stop screw then makes the TPS see the wrong voltage per TB blade position. For people who do this with aftermarket TB's in a attempt to get them to idle right (because their IAC counts are pegged) they then "slot" the 3 holes in the TPS so they can "clock" (position) it back so TPS reads .67vdc in the new closed position and 4.5 vdc blades fully opened.
 
#9 ·
what does your idle sound like now? With the cam I'm running in my H/C/I LS1 900 is basically the lowest it will maintain a steady idle, it sounds pretty lopey, its basically all about what the cam will handle, if it sounds smooth or fast it may have a vacuum leak.. do you have access to a scan tool? At least that way you can see what the desired idle is set to.
 
#13 ·
The car is an M6, currently not able to check the IAC or or anything else as I am not at home, but I do know that the throttle has been played with in the past because someone owned this car for a short period of time, and in that time period, they touched more things in a wrong manner than a corrupt priest in a daycare center
 
#16 ·
Back it off until the butterflies begin to stick in the bore when you snap the throttle closed. Then tighten it until they stop sticking. Lock it down and leave it there.

I know that you have a 6 speed, and there's no line pressure to worry about. Just having a discussion about it...
 
#18 ·
Whatever you can get to fit. I don't know how yours is configured. You may have to pull the TB to get to it.
 
#23 ·
I think I still have the stock TB kicking around the shop somewhere. I'll see if I can find it and look, otherwise, you'll just have to pull it off and look.
 
#22 ·
If you're closing the throttle to correctly adjust the throttle plates, it will bring the IAC counts up. You also want to make sure all of your idle air (except for what is bleeding around your properly adjusted throttle plates) is going through the idle passages in the intake manifold.
 
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