2013 ZL1 idle issues. What affect does clutch position have on idle control?

[Tick]

I'm having trouble getting the return to idle sorted out on a ZL1 that came from another shop with these issues. Basically, it will idle dip, surge, or hang when coasting and pushed into neutral with the clutch engaged (pedal released). Idle is good when sitting still and start up is good, adaptive timing is tight. But depending on the style of driving, the car never returns to idle good or the same when coasting.

If the clutch pedal is held down to the floor while coasting the car will return to idle fairly good....and if the pedal is held there till it has came to an idle rpm it will idle good even with the clutch pedal released.

What affect in terms of idle control and/or timing does the clutch position have?

I've played with the base running airflow table and etc scaler all of over the place with multiple combinations and I can't get it to return to idle worth a crap. I've logged airflow and pasted that into the base running airflow table as well minus varying percentages....nothing seems to help. Right now I've got it in speed density mode using a vve table I built from another similar car and the fuel trims are within reason. By running it in SD, I was able to straighten out a ton of timing fluctuation at idle but the drivability remains the same. The car has a custom cam, cnc'd heads, pulleys, long tubes, LS3 tb, etc.

[Tick]

Starting at frame 2970 you can see how the car returns to idle. Idle basically drops to where it should be, then it flares up a 150 rpms or so. The tps position shows that the tps increases about 3% which would seem to be the cause of the rpm flare, even though the timing is being pulled all the way down to 1 or 2 degrees in an effort to combat the excessive rpm. Earlier in the log the car surges really badly (around frame 578) and was how the car responded to a shift to neutral and clutch engaged before the engine comes back to idle. At around frame 1500 you can see how the car behaves if you hold the clutch in for the duration of the rpm flare... Another strange thing to note are the STFT's during these episodes. I'm not sure why it would feel the need to add nearly 30% while the o2's are pretty much pegged rich as well as the wideband. With that said, I have seen less surging in SD only (maf was back on in this log) and the trims don't do that either in SD, but it has never been acceptable no matter how I adjust the raf or etc scalar.

Why does the tps bump up like this when clearly it needs to close if anything?

[Tick]

Don't pay attention to the PE/wot portion of the tune..... I haven't worked on that yet lol. A raped PE MAF only tune with stock MAF data at WOT from what I thought was a very reputable shop.

[Tick]

When is the coast down timing table used? Is it even used on a manual trans car?

I have read that when coasting at idle the HO table would be used for timing and that the main timing tables should be matched to the idle table to eliminate a big step between the two.....but clearly from my logs when coasting at idle there is adaptive timing adjustment coming into play. I have read that the idle timing table isn't referenced until the car stops moving, but that just doesn't seem to be true on this particular ecu. Besides that, matching the timing tables will do more harm that good on this vehicle if I'm not mistaken because the main table becomes an 'upper limit' to what the adaptive can add to the base idle timing...

It also seems that having the clutch engaged or disengaged makes a very noticeable difference in the idle stability when coasting..... Keep the clutch pedal down and the idle is much more stable. Either engaged or disengaged doesn't seem to be using the HO table though...

I can log adaptive idle timing on average and get very small numbers if the car is sitting still. Timing is really smooth with the MAF disabled and adaptive barely has to adjust anything. This would lead me to believe the raf is pretty close at idle. However, if I go into the scanner and turn the 'spark idle' to 'on' the idle will surge getting progressively worse until the car stalls. The throttle starts trying to control the surge it seems which only adds to the surge.

This car came to me with an LS2 throttle body on it.... I was sure that must be the issue based on everything I've read about guys running into issues when mixing these up, mainly guys who have a c5 who need to use an LS2 but try an LS3 because they are cheaper or whatever. Not sure I've ever heard of anyone installing an LS2 onto a newer vehicle though. Either way, I swapped to an LS3 throttle with no real change in how the car returns to idle.

This is my first ZL1 tune, but I've done a few cts-v's and a ZR1 that I really didn't have any of these issues with. I've tuned a bunch of LS3 vettes and Camaros...... I have no clue why I can't just dial in the raf like every other car and get an acceptable idle. Any ideas would be greatly appreciated. At this point, I'm willing to pay for the information that gets me pointed in the right direction. Maybe there is something special that needs to be done in terms of the LS3 throttle other than changing the raf and etc scaler?? Maybe a trick to calm down the throttle movements when coming back to idle?? Throttle follower torque??

[jon6.0]

Did your customer keep their stock throttlebody to swap back on maybe?

[mowton]

Did your customer keep their stock throttlebody to swap back on maybe?

Not at a computer but certain os' s will deactivate the throttle cracker and or follower when clutch is depressed during decel/coast down.

Ed M

[edcmat-l1]

Not at a computer but certain os' s will deactivate the throttle cracker and or follower when clutch is depressed during decel/coast down.

Ed M

E67. No cracker. And rarely does the follower need to be modified in these cars, but in this case it may need to be.