I'm working on high idle issues as well and just ordered my diagnostic cable so I can run scans and check numbers. But I believe somewhere in one or your posts or threads you mentioned that when you're idling and rev your engine the rpm's float and stay high? Mine did that beforehand and it was vacuum leaks. I fixed them, which included the intake manifold, and I don't have that problem anymore. The only thing I need to do now is run my scans and check the idle steps, tps voltage, and a few other things to get it under control. Your problem may lie somewhere in there as well, just a thought.

 

I will try and check them again, but as far as I could tell it seemed as if everything was plugged up correctly. but im not 100% sure. I may need a second pair of eyes to help me look. Im really trying to correct this idle isse. Im just curious though, if it was vacuum line, would it run at 2000rpms when clutch is pressed/in neutral and only go back to idle (which for me is 1200 rpm ) when im fully stopped? I dont understand why it only idles high while car is in motion but once fully stopped it idles back down to 1200 which is still high idle.

*wait what you mean fixed intake manifold??

 

My manifold leaked, I replaced the gaskets as well as several hoses. before doing that, my idle would be very high fluctuating around 1800-2000rpm's sometimes higher even while driving and also while just sitting out of gear in my driveway. When i took it for drives it would still be high and take forever to come back down when stopped at a light. For me the vacuum leaks and manifold problem is what was causing it for me. Now I'm just stuck with high idle without the fluctuating numbers or floating rpm's after I rev the engine. I believe I just need to reset my IAC steps and check my tps. I hope.

 

Well if you get it figured out please let me know!! imma check my manifold and stuff tomorrow and see if i can find any leaks!

 

carb cleaner spray it up and see if idle changes to detect some leaks

 

If he doesn't see any leaks visually he may need some scanning software so he can view real time data when he sprays the carb cleaner. When we sprayed mine with the high spurratic idle like his we couldn't tell any difference yet when hooked up to the snap on we saw the numbers fluctuating.

 

I thought he mentioned that he found a tear in the air inlet elbow??That would be the first part to replace,these Lt1s are very touchy.

 

The tear wasnt bad at all, and it actually seals really good, so im eliminating that out of my problem. I do want to buy a new one though, do you need the long tube that hangs down in front (silencer thingy)??
Hopefullly thursday morning Ill be able to take it to the shop and hook it up to snap on machine and really see whats going on!!

 

Found two vacuum lines that werent plugged up but i cant find where they go or what they are to? please help. and dont 4 get about this is lt4 swap.

 

Go to shbox.com the site has a ton of information as well as diagrams of almost everything you will need.

 

In the top picture, that is fine(provided that the other two hoses go to the correct spot)....it's just mounted the wrong way. Picture...



For the pic below...I think the EGR is above the PCV connection and Opti connection below the EGR. Are you missing a port on the LT4 intake manifold because it did not need EGR?



For reference....

 

I figured out where my vacuum leak was!!! Damn pipe that runs to PVC breather hose didn't have a clamp on it and it had fallen out but since it was tucked under intake n behind intake elbow I couldnt see it. But got that fixed today!! Now it doesnt idle high when I put it in neutral while driving! It idles back down to about 1000rpms which is where it is idleing now (still to high?) so problem one fixed! Now I looked on throttle body and the idle screw on it sticks almost half inch out (normal for bbk tb??) I also found out the water pump has a tiny leak on the backside seal of it too, and front seal has a very very small leak nothing to hopefully worry about yet! So you were right idling up high was from vacuum leak. Now if I can just get this thing to idle about 800 rpms I'll be happy

 

Do you have a scanner of any kind? Would be the best way to do it. Could check your idle counts that way.

 

We put it on snap on scanner today and a vertronick(spelling??) and all it told me was what car was idling at not what stock settings were. I don't have a lt1 specific lt1 programmer or anything and don't know of anyone close that can check any of that. Plus it's hard to check with those bc it's a 97 lt1 but has lt4 top end and custom PCM from GM. So... Kinda lost on what to do

 

What idle speed did the scanner report? I doubt your PCM is custom. More than likely, it's a F-body PCM with a custom tune in it. I've got a 96 factory manual. I'll try to get snapshots of the troubleshooting chart for a high idle.

Do you know who tuned the PCM?