Have been having some issues with my c5 corvette idling and sometimes it will die rolling through a light in neutral or taking a turn slowly. When it stalls it won’t restart unless I give it some gas and it won’t stay running a lot of the time if I don’t give it any gas, and the idle surges 2-300rpm up to 1,000rpm when this happens occasionally. These issues all started a bit after I did a major engine overhaul and put in a state 3 btr cam .636” .636” lift 227/240 111.5 Lsa, CNC as cast ported aluminum cylinder heads (63cc chambers) Lsxr102mm intake, speed engineering longtubes and x pipe high pressure oil pump etc. Got the car tuned by Nick at newtech performance hayward Ca. He specializes on Ls1s. Car is running on speed density so it DOES NOT USE THE MAF SENSOR. I cleaned all of the main engine grounds with baking soda vinegar sandpaper and a wire brush. I changed from the 1998 style with the incoming fuel line and a return line just to the regular single return line and changed to the later style regulator, replaced the throttle position sensor, cleaned the ignition contacts, put a new Tac Module in, checked fuel pressure (60 psi) at idle and it dosent bleed down. Fuel pump is working i can hear it prime, sprayed around intake for vaccum leaks, battery is good cranking at 12.5 volts and it stays above 12 volts 24/7. Put in a new starter, Throttlebody is as clean as a whistle. What could it be? I have the PIDS from my scan tool I will upload of the Map sensor readings and fuel trim at idle with the key on and above 3k rpm. If anyone has any ideas i’d love to hear them. I don’t want to throw any more parts at it and need this fixed once and for all. Very confusing 🫤

 

It's likely in your tune if everything else checks good. Idle tuning is the most difficult part of the tuning process, at least to me. A lot of people have hanging idle and idle dip issues that they ignore or struggle to fix.

Do you have tuning software you can make changes? Some people on here who are very good with tuning help.

I know no one likes to hear it's in the tune when they have the greatest tuner etc. I had mine done by a guy who is very well regarded and still had to make many changes myself. I think it's a lot of copy and pasting in the industry.

 

This is simple its your tune. Im best advice to you is ask if the next tuner specialize in driveable and idle tuning or your going to be in the same place. I've been through this they are lazy and it's tedious to get drivable go enough to where you don't get frustrated driving the car.you have get it to another shop to get it to the point where it's ok not perfect but very acceptable. The shop i went to couldn't even get close. So i bought HPTuners and leaned and my car is perfect. I called them back up and told them that so many paramature were not even touched from stock setting that affect idle and drivable. And they kept with their original statement that it was mechanical and i changed parts to get it to work. I don't even want to tell you what i told them about their business. ANd yes i build the engine from ground up. There are parmatures where it effects exactly the problems your having. These are the tuffest paratures to tune.

 

It sounds like a tune problem to me as well.

That cam has a fair amount of overlap, and overlap makes idle hard to tune.
With that manifold I'm guessing that you also have a 92 or 102mm throttle body, and those also complicate idle tuning and startup.
If you've also got a lighter clutch then that's the idle trouble trifecta.
And the symptoms are all pretty similar to what my car was doing after I upgraded the cam + throttle body + clutch.

I'd start by describing the problem to your tuner and asking for an updated tune. It might take a lot of iterations to get it to idle (and return-to-idle) (and cold start) (and hot start) consistently. Especially since it kinda sounds like your tuner might not have a great understanding of idle tuning to begin with.

If your tuner can't do a decent job of this, then your other options are find another tuner or start learning to tune yourself. The nice thing about idle tuning is that there's very little risk involved, so it's not a bad way to get started with tuning. But on the other hand it's also hard to get right, since there are a bunch of interacting features, and a bunch of different scenarios to test, so it can be kinda frustrating.

The worst part is that there were so many times when I thought I finally had it all worked out... and the next day it would stall or surge or whatever.

After I found a strategy that I was finally happy with, I wrote about it here: https://legacynsfw.github.io/idle-tuning.html

 

Really appreciate the feedback guys thank you for that attachment of info. I took it to a tuner that does more diagnostic work who also has a shop and dyno and he is a real good tuner. Fingers crossed we will start to get this worked out. Currently I have the stock 72mm throttlebody because I bought one that ended up being a gold blade for the Ls3s and later not silver blade so it didn’t work and I put the stock one back on. Eventually i’m gonna get HP tuners so I can learn to tune it myself and make adjustments. I’ve never tuned a car before so I’ll have to learn that whole process.