Alright in Park and Neutral the lt1 is idling at 1300-1500rpms. I cannot figure it out. Checked for vacuum leaks at brake booster, ac, etc. and its good. Took throttle body off and cleaned it well and took out IAC and cleaned it also. Still idles high.

Only mods are hotcam, springs, 1.6RR, Extreme timing chain, high volume oil pump, custom intake, street and performance headers, no cats, true 2 1/2" duals with dynomax bullet mufflers and turndowns.

Something me and shoebox have been talking about is the PNP Signal from the PNP Switch to the tranny. I dont have that hooked up and I am thinking that may cause this problem. It runs 60mph at 1900rpms (3.42s), and idles down at stoplights to 800rpms in gear. If anyone can shed some light on this issue, please do.....

 

When you were cleaning the IAC, did you turn the key on and make sure it toggled back and forth before reinstalling it?

quick check to see if it's the iac or not, ball up some masking tape and place it between the throttle blades in the throttle body on the bottom side to block off the iac hole. If the truck won't idle and you have to use the throttle to keep it running, then you know the iac is stuck and that's your problem.

I had the same problem w/ my truck, the iac was frozen solid after sitting dormant for so long, it would get up enough nuts to move every once in a while when it was warm, but for the the most part is was stuck wide open. New IAC, and it runs and idles great! Did you clean all the oxidation out of the IAC hole when you cleaned it? My aluminum tb was nasty inside.

I don't have my pnp hooked up and it runs just fine, it just won't idle up when I put it in park or neutral, stays at 550 all the time, I'm pretty sure that's all the ecm is using it for, besides starter safety and reverse lights.

If you have any pics of your truck anywhere, I'd like to take a gander at your install and the intake you did.

 

I didnt check the iac to see if it was working or not. I was fairly nasty, and i cleaned out the TB too. The motor has sat for a year atleast. Are you suppossed to be able to move the IAC at all cause i tried and couldnt push the spring down.

I will get some pics up, but some are up at http://www.sounddomain.com/id/gmc350ss

My intake for now is a straight 3 1/2" PVC pipe painted black with a cheap blue and chrome filter I grabbed off ebay for 5 bucks.

 

no, the iac shouldn't move. just pull the intake, wad up some tape or something, block off the hole in the bottom of the tb going down to the iac, put the intake back on and fire it up. if you have to keep your toe in it to keep it idling, you found your problem.

man, your truck looks awesome!!! where did you get the rubber piece to connect the maf to the tube? right now I just have a huge K&N RE-0920 hanging off the maf.

good luck man.

 

Don't try to move the pintle of an old IAC by hand. That can strip the worm gear inside.

 

my motor sat for about a year as well in my garage, but it was real humid, noticed rust on the neck of the iac, motor is probably gunked up.

I tried to move the old iac, but it wouldn't, got a new one and didn't move it for risk of breaking it.

sorry, forgot to add that.. was in awe of the pics.

 

do anything to the TB....maybe the idling cables? are the cables allowing the idle to close all the way?

 

Hotwire, thanks for the compliments. You can get the rubber adapter anywhere, I think I picked mine up at home depot. It's just a 3" x 3" rubber pvc splice. works perfect. I will block off the iac hole tomorrow morning and see if it wont run and I have to tap the gas.

Shoebox, I didnt try to move it very much at all.

FacelessZ...what are the idling cables?

 

think he was referring to the gas pedal lines. see if they are binding up on anything, see if your tb blades close all the way...

let us know what you find man, hope it's a simple problem.

 

Yea the throttle cable is fine and the TB is closing all the way. I gave it a good cleaning so the blades arent sticking. Will cheak the iac in the morning to see if it wont run if its blocked off. What does this prove though? that its allowing too much air in???? if it runs still with the iac valve blocked off, then I have other problems right?

 

You are correct. You are blocking the air supply off to the IAC, it's basically a controlled vacuum leak. If you block it off and the truck needs a little pedal to run, then you found the problem, replace the IAC.

If it still idles high, you have problems else where.

When did this come about? As soon as you installed the motor? After the RR install? etc.. If it was right after the motor install, I'd put money on the IAC. If that's the problem, and you do replace it, don't forget to lube up the iac and the iac port in the tb w/ motor oil to keep if from happening again.

good luck.

 

Well for the first 5 or 6 mins the truck idled at around 800, but then it was always high after that. At first I thought it may have been the lack of o2's, but I guess not.

 

luke,

just a reminder. if you get the iac and all sorted out and it still idles high. think about gettin that aldl hooked up0 and go see if your boy at GM can hook it up to a Tech-II scanner/tool it'll tell you real time stats, and can possibly lower your idle the easy way.

Brandon

 

Well I blocked the IAC as best as I could (probably 90 percent blocked), and crunk it up cold this morning. Idled at about 700-750rpms. This was not on a warmed up engine. DO you think that the iac is the culprit?

 

try getting it completely blocked so you know for sure. i wouldn't feel comfortable in saying it was the iac till you know for sure. get it completely blocked and refire it. you have to completely eliminate the possibilities.

I even took some tape after I balled it up and ran it across the intake where the hole was to be sure it was sealed, just make sure it doesn't interefere w/ the throttle blade operation or intake duct sealing.