Return-to-idle tuning

General Tuning Questions And Discussions
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Re: Return-to-idle tuning

Postby VK_3800 » Tue Apr 07, 2020 9:00 pm

In theory but I've already got the throttle stop open to absolute max now, under some conditions it will completely close the IAC and still idle a touch above target. However many other times it needs more steps just before moving to closed loop idle, especially if stomping on the brakes. PCV is also a factor here as its a controlled leak, changing to an adjustable valve that allows fine-tuning to suit the cam helped give a bit more control.

Its not a matter of the IAC not reacting in time, no changes are commanded unless its in closed loop idle or one of the transition situations as discussed above applies (but often none do, or its hard to strike a balance as above). Even with the delay for closed loop idle set to 0 it still takes a moment for the stop to register (is there a way to set a max road speed for idle?) and the change to occur, plenty of time for it to drop to very low rpm if not stall. It doesn't take much to drive around this but with a good EFI system it'd be nice to tune it out completely.

Not sure how people with actual big cams (like 260+ @0.050) get on with this? I guess they are all running 1200rpm idle with high stall autos.

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Joined: Mon Jul 11, 2016 6:29 am

Re: Return-to-idle tuning

Postby Wade » Sat Apr 25, 2020 9:08 pm

Yeah I’ve played with tuning cammed ls1’s. It’s a pain cause once you play with one thing you’ll find your chasing your tail and having to adjust everything else. Main things like normal are more idle timing, higher idle rpm and than give it some more idle airflow. But than cracker/follower and all the rest start not behaving so it’s round and round we go. I ended up just drilling the throttle body hole out a little which saved me from really having to do any more work. From there it was as easy as just making little subtle changes to gain the characteristics I was after

Posts: 562
Joined: Mon Jul 11, 2016 6:29 am

Re: Return-to-idle tuning

Postby Wade » Sat Apr 25, 2020 9:17 pm

If you look through all the 300kw hsv tunes with the callaway engine the early tunes are a bit more extreme in the idle department compared to the later ones. It’s good to see how holden tuned them over the years

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Re: Return-to-idle tuning

Postby jlvaldez » Tue Jul 14, 2020 4:45 pm

Just noticed there's a tuning section on this forum.

Overall good feedback! I've done a lot of LS tuning for Gen 3 and 4 LSs, but entirely with HPTuners and EFILive. My whole reason for using this open source stuff was to hack the lean cruise ;)

Everything you said, I agree with.

I'll chime in with a few extras, regarding throttle follower and cracker.

I normally 0 out cracker, and use follower as my "Dashpot" throttle for quick transitions. For example, with quick throttle blips, sometimes things come down too quick and you'll undershoot target idle. I find that by adding some throttle follower will keep some of that throttle % and decay it slowly to help cushion the return to idle.

Regarding your spark tables. Be careful with your idle and main spark advance tables. I find that if you have them too different, you'll get very unstable/bucking behavior when you start from a stop in a manual car (as your spark will suddenly jump up) and if you're doing cruising, you might get a lot of bucking as you switch between idle and main spark tables. I believe default tune will refer to the idle spark advance table anytime the throttle is closed, not just speed (though I might be wrong). Remember this relationship because more spark = less base running airflow is needed to maintain an RPM. What this means is if your main spark table is selected based on speed alone, then when you're moving and let off throttle, your RPM will tend to hang because you may have a 10-15* difference between idle spark and main spark. I actually use this to my benefit on fussy cammed cars as a way to hold a higher idle while cruising because rolling idle seems to be unpredictable.

Don't worry too much about getting idle perfect if your fuel isn't dialed in. Modified LSes are quite sensitive to AFR (at least the ones I've touched) and tend to surge a lot when rich or undershoot idle when lean. Keep in mind that if you have long tubes, you should also adjust your PID for closed loop fuel at idle :)

As a note regarding start up and idle tuning, I made a thread with some of my experiences many years ago on the HPTuners forum. I'd do some things different now, but I am not a professional tuner, by any means. I just do it for friends and my own vehicles (and help some on line)

And again another thread for how I tuned the ETC scalar for a larger TB using datalogs instead of guessing with numbers people post online


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