Rolling Idle Issue 03 Z06

[the1n_only]

Im helping a friend of mine with his 03 Z and the issue is when rolling you clutch in the RPM will hunt and surge. At times the car will die. If you throw it into neutral real fast it will settle down quickly and the idle will stabilize. When the car is not rolling there is zero issue with the idle. It will instantly fall right into the commanded 950 RPM.

The car is a 441ci with ported LS7 heads and a 248/256 cam. The issue showed its ugly head when he swapped from 1 3/4 headers to 1 7/8 and also at the same time going from a Spec twin disk to a Ram that was a little bit lighter.

attached is the tune. Advice would be appreciated

[printmanjackson]

I have a thread where I addressed the same problem. Clutch in and idle drops and searches. The problem is it needs more air.

I was able to correct the problem with the Rolling Idle then look at the Airflow Adder table. Start with something like .20 across the board then go from there.

[the1n_only]

Thanks

[LSxpwrdZ]

Yep and I also see that you have Cracker disabled which is another source for rolling idle airflow adder. I honestly would shrink some of your LTIT max/min down some as well. +/- 6g/sec is alot of learning room. +/- 1-2g/sec should be plenty of learning distance.

[mowton]

There is a thread below on this subject. The Vette disables the TC and TF upon clutch depression so you would have to use the Rolling Idle tables to emulate that function. I have heard (and experieinced) the lighter flywheel is the culprit as it doesn't "store" kinetic energy to help decel the engine at a controlled rate. My new theory on this (thanks to your post and relaxing on vacation ) is depressing the clutch on a setup like that creates a very large drop in torque. This is in direct opposite to the increase you realize when the AC turns on I would summize.

In your tune I see the ETC area scalar is larger than stock which would mean you have installed a smaller throttle body. I would doubt this as I would guess you have at least a 90 mm which would use a .0192 scalar. But as you stated, all was well before the header/clutch change so I will leave it to you whether you want to re-tune with the correct scalar. Also make sure your VE and MAF are spot on in the idle area's with out the aide of Adaptive idle as this simulates the rolling idle scenario. Adaptive idle doesn't kick in until speeds less than 1 mph. Make sure the LTIT is very close to zero (RAF/Scalar) so there is little transition from the the clutch engaged to the clutch depressed or rolling idle condition. Want the PCM to recover very quickly from cruise to idle and you don't have the assistance of TC/TF or Adaptive idle.

So getting back to the clutch, if theory serves itself right.....if you need more air/spark to compensate for increased torque then I would think you would need less air/spark for less torque. Just a thought...not proven

Oh well...back to my vacation

Ed M

[edcmat-l1]

There is a thread below on this subject. The Vette disables the TC and TF upon clutch depression so you would have to use the Rolling Idle tables to emulate that function. I have heard (and experieinced) the lighter flywheel is the culprit as it doesn't "store" kinetic energy to help decel the engine at a controlled rate. My new theory on this (thanks to your post and relaxing on vacation ) is depressing the clutch on a setup like that creates a very large drop in torque. This is in direct opposite to the increase you realize when the AC turns on I would summize.

That's right Ed. The TF and TC tables are actually IAC tables, and don't really work in the ETC cars. At least not rolling, clutch in.

BTW, I was the guy who found the rolling idle tables and got HPT to add them to the software. I'll break my arm pattin myself on the back for that. LOL

On the light flywheels, yep they can be a major pain to get right. There are some definite "tricks" to tuning them. Problem is, as I see it, the engine decellerates too quickly, causing either a bad idle dip and stall or it sets off the stall recovery, and subsequent surge, where it gets into the fuel trims swinging, and timing rolling and can't recover until the car comes to a stop, and the idle controls take over.

I wish there was a switch or something (enable/disable master) to allow idle controls while rolling. I have yet to find it, or find any indications of there being one in the GEN 3s. I've been trying for years to set them up to go into idle strategy while rolling, with the clutch pushed in.

Oh well...back to my vacation

Ed M

Have a great vaca. Hope you're somewhere warm!

[mowton]

Have a great vaca. Hope you're somewhere warm!

Thanks Ed. It is supposed to be but woke up to 54 degrees. Both my kids say we brought the cold temp to the south :-( But still warmer than home :-)

Have a great weekend

Ed M

[LSxpwrdZ]

I wish there was a switch or something (enable/disable master) to allow idle controls while rolling. I have yet to find it, or find any indications of there being one in the GEN 3s. I've been trying for years to set them up to go into idle strategy while rolling, with the clutch pushed in.

Thats why I love Fbodies as far as idle routines go. I've found that most of them will re-enable adaptive idle routines when you get under the TC speed. I had a flare problem on my Formula that was caused by the stall acting like a rubber band for the idle flare and raising the TC enable speed to re-enable adaptive idle cured every bit of it.

[edcmat-l1]

Thats why I love Fbodies as far as idle routines go. I've found that most of them will re-enable adaptive idle routines when you get under the TC speed. I had a flare problem on my Formula that was caused by the stall acting like a rubber band for the idle flare and raising the TC enable speed to re-enable adaptive idle cured every bit of it.

Yes, but they still don't use the idle routines, as in over/underspeed spark. That is the THE tell tale. If your under/overspeed isn't working, it's not truely idle mode. Another key indicator is your idle trims. If it's not using STITs, it's not in idle mode.

At least this has been my finding. Do let me know if you're seeing something different. I've been experimenting with different idle strategies for years, and am always looking for new data, or techniques.

[LSxpwrdZ]

Yeah I stumbled across it on my personal car actually. I'll post the tune file up for you tonight when I get home but it is a standard '156 OS auto file from my car and it re-enables STIT and idle under/over spark when speed goes under the TC disable speed! I'll also try to take a spin in the car tonight to show you a log as well.

[the1n_only]

The rolling idle tables did the trick. they make things a lot easier

[LSxpwrdZ]

Haven't been able to get a log for ya to show the STIT and Idle Spark re-activating under TC setpoint but here is the tune file from the car...

EDIT: I added the log and config file to look at.

[LSxpwrdZ]

Okay I finally got a vette in today that I had worked on before to see how some of these tables worked on and the TC and TF was working on it rolling clutch in or out. Now I'm not sure if his clutch switch is even working because this car is kindof hacked up but I did a short log of it today as well to show that the TC was operational and that the rolling idle did not work.

Disregaurd some of the idle dips, this car had a really weird clutch and I about stalled the durn thing a couple of times during this log haha.

[ProjectD]

LSxpwrdZ Thanks for posting your findings w/ the F-body pcm. Do you know if the same thing applies to an 04 GTO pcm?

[LSxpwrdZ]

I will have to go back through some logs to verify the similarities on function but I'm fairly sure they do operate similar to the Fbody being IAC controlled car's like Fbodies.

[edcmat-l1]

Very interesting. I would almost swear I've tried raising the TC speed, but can't say positively. If I have I've probably done it in a Y body. I'll have to try it again. Got an F body to do today. I'll see how it works.

Thanks for posting it.

[RSTinOKC]

This thread is a godsend!!! I have been chasing my tail for months trying to fix coast down dipping idle to no avail. To make matters worse I was getting this in a 5 spd truck, so as you can imagine, finding information on this in a class dominated by auto transmissions was difficult. I need to fine tune it but at least now I'm not taking blind stabs at it...thanks guys!!!