Help me stabilize idle

[traviz06]

I have played with this for a long while and cannot get the idle to stablize. I have tried everything that I have read about. If someone could review my datalog and my tune, please offer assistance. It is annoying to get a swinging rpm idle all the time Whether I move the base idle airflow up or down makes no difference along with various afr's and timing. What am I missing?

this is the closest I can get it. IT will stay steady around 850rpm and then start swinging +/- 50 or so rpm before stabilizing again. Also when I start the car, there is high rpm flare-up, like 2k rpm before it comes back down to 850ish idle.

this is a 02 c5z, ecs small blower cam and vortech v3 supercharger. longtubes, no cats. 2bar map no maf.

[1slowbusa]

Why is the spark constantly at 20 degrees. That makes me think the idle adaptive spark control is not working but as far as i know the only way to disable that is with the vehicle controls in the scanner or zeroing out the idle adaptive spark control tables. But i see you dont have those zeroed out.

[mowton]

Its stuck in the main spark table and not in adaptive idle. Set the TPS Min back to 1.2% and increase the main spark table to 10-12 degrees above the base idle in the idle rpm-g/cyl so it doesn't constrain the 20 degrees you have set for the idle spark. I know certain platforms will limit the idle spark to the main spark and hog tie the adaptive control.

Also, as you have essentially disabled the adaptive idle spark control, you can see by the surging that you need to work the idle adaptive PID airflow corrections. This is how we explain idle tuning and make sure we have set the airflow corrections as best as we can and then the spark correction doesn't have to work as hard...Not sure how big a cam, but if overlap is medium to significant, then you need to "reduce" the authority of the adaptive air and spark to allow the cam its natural rpm/lope swings. If too tight, you create instability....

Ed M

[traviz06]

Thanks guys! I'll make the necessary spark adjustments and reply back with the outcome! I didn't know that the main spark table is the upper limit allowed, probably why adaptive idle isn't working.

I am not sure what you mean by the adaptive PID airflow connections. Do you mean base idle airflow?

Lastly. My cam is quite small, ecs describes it as a small blower cam in the 220's duration, .580 lift and 115lsa

[cobaltssoverbooster]

no, raf is just the base line running airflow table.
PID tables are basically sensitivity controls for the automatic adjustment feature in the ecu.
unlike idle advance where you can program ignition values for the amount of rpm over or under, the pid table uses the raf as a desired target and when it swings over or under the pid table acts for you. you get to tune the pid controllers sensitivity basically.

if the cam surges and the idle air motor doesnt correct it very fast then you make the pid controller more sensitive and it in return makes corrections faster/sooner/more agressively.
and of course vice versa applies here too. overdoing the correction would require slowing the pid corrections down.

not the easiest type of system to describe.

[wasyl]

Idle Spark Advance In Drive/In Park is messed up

best regards

[mowton]

Idle Spark Advance In Drive/In Park is messed up

best regards

They are both the same...why do you say they are messed up? Drive could have 2-3 degrees more to increase torque while in gear and foot on brake.

Ed M

[mowton]

no, raf is just the base line running airflow table.
PID tables are basically sensitivity controls for the automatic adjustment feature in the ecu.
unlike idle advance where you can program ignition values for the amount of rpm over or under, the pid table uses the raf as a desired target and when it swings over or under the pid table acts for you. you get to tune the pid controllers sensitivity basically.

if the cam surges and the idle air motor doesnt correct it very fast then you make the pid controller more sensitive and it in return makes corrections faster/sooner/more agressively.
and of course vice versa applies here too. overdoing the correction would require slowing the pid corrections down.

not the easiest type of system to describe.

So to clarify (because sometimes I type too fast :-)), the RAF is established as the minimum throttle opening. The adders like Friction, Startup, Throttle Cracker, Throttle Follower, AC, Fans etc are added/subtracted from the RAF value to develop the required TPS% (actually it is calculated to mm2 and then transformed to TPS% for DBW and IAC steps for DBC). Additionally the PID airflow values are added to make the Adaptive Idle airflow corrections. These are represented by the LTIT and STIT parameters. So one very important factor in Gen III Idle tuning is to make sure you put the airflow values into the correct buckets so they are available when needed and are decayed out when done so the final airflow requirement is correct for all scenario's. An example would be is if you had startup issues and you put the extra air into the RAF table. The car would start better but after startup that extra air would remain and possibly make the idle hang or worse, make you go take air out of another incorrect bucket and continue down the destructive idle tune path :-)

As the idle is constantly changing (especially with larger cams), you want to make sure your MAF and VE tables are dialed in, especially in the idle area. To perform idle tuning you always want to remove as many airflow variables as possible to isolate the PID effects. This would mean turn off AC, Shut off the Fans, no pedal hits etc. Now the the PID values can be adjusted based on their contributions where Proportional is real time error correction, Integral is more a rolling average over past and future predictions and Derivative (the harder of the three) is based on rate of error change...the faster the error change the lower the airflow error contribution.

Again you want to disable the adaptive spark to determine the quality of you airflow tuning...get it the best you can that way and then re-enable spark and it gets that much better.

Ed M

I find adaptive idle to be the most interesting and challenging function we have to tune. That is why our tutorial contains a 43 page Module on Gen III and Gen IV idle tuning :-)

[cobaltssoverbooster]

Thanks for the post Ed. I understood it but you say it so much better.
At least i took a shot at offering an explanation. I tried.

Much appreciated.

[traviz06]

Thanks for all the updates. I should have replied sooner. I wanted to let everyone here know you have been a great help. I am still unclear about this adaptive PID connections, unless it is just a way to define the combination of all things idle-related. Anyways, I changed my TPS % to 1.2% stock as I am not sure when or why I adjusted it but I forgot about it. Also, I copy and pasted my original z06 idle timing tables and it suddenly idles great again. Super steady at 850. I have not datalogged it since nor have I done a RAF adjustment. But as they say, if it's working, don't mess with it, right?