MSUGTO

Back in April I completed a H/C/I swap on my 02 Z06, got it tuned and have been very happy with the car. Only thing that I don't care for is the fact that 9 times out of 10 when I am coasting to a stop with the clutch pushed in, the engine will maintain 1200-1500 RPM but the second I come to a complete stop, the engine will drop to the correct idle speed.

I've done some digging around on the subject and read about a few guys disabling the throttle cracker and follower. Figured it couldn't hurt so I did that and love how the engine comes back to idle more quickly and directly back to the correct idle speed without any sign of the idle speed hanging whatsoever. However, sometimes the engine will also drop way past idle speed and sometimes die. Any way to prevent this? The tune is attached for you to look at.

Attached is the current tune and the specs of the H/C/I swap are below:
Tick Performance SNS Stage 3 235/243 .630/.610 111+2
TEA Stage 2 head work on 243's
FAST 92
LS2 TB
1-3/4" LG Super Pro's

Attached is a scan I just took and the hanging idle didn't seem to be as bad today, I've seen it hang around 1500-1600 RPM. At 14:43:00, 14:44:51 and 14:46:00 you can see where the idle is hanging and then drops to the correct idle speed when speed is 0. It looks like timing drops to almost nothing each time idle returns to normal.

As far as the scan goes, for one reason or another I couldn't get desired and actual airflow to populate on the chart vs time section but it did show up correctly on the channels section.

Any feedback would be appreciated, thank you.

tblu92

A hanging idle is very common with any hds cam engine due to the added airflow---
However this is an easy fix for a tuner with HP or EFILIVE
Most often it can be fixed using the"Throttle Follower table" in your tune----
ADDING a % to the throttle follower table should correct a hanging idle---
I would start with like adding 10% to the entire table "in gear"
2ndly if you had the car tuned after the H/C mod your tuner may have added to much air to your "desired airflow table" which also can create a hanging idle----
Try the follower 1st --if that doesn't fix it SUBTRACT 10% to the desired airflow table in gear----- On both these adjustments if you go too far you will get the opposite affect--dying !! This is strictly a trial and error method and cannot be done mail order to fix in one attempt

rriddle

THank you for the feedback. Do you suggest disabling the kracker to make these modifications or would that be left stock?

tblu92

is is a trial and error thing some cars run fine with the cracker and or the follower dis abled--- My guess is that most work best with an adjustment to the follower--The cracker adjustments seem only needed with a larger than stock T-Body

Chevy Guy

Isn't there the thought that you can/should pull timing as the idle drops? Looks like there is some odd spark activity while the idle is dropping.

rriddle

Pulling timing will, in essence, drop the idle. Adding timing will raise. If you see the timing dropping it is probably due to too much air and the timing is the fastest way for the adaptive idle to compensate for the RPM gain or loss.

Chevy Guy

The log shows that the timing is spiking during idle down, looked odd to me, but I'm nowhere near skilled in tuning.

rriddle

Neither am I. I'm just learning myself. Based on your feedback it would tell me that the adaptive idle was trying to compensate for idle being too low on the ramp down which could mean it needs a bit more air.

tblu92

Another issue common with mods like cams etc is the "DFCO" this is the deceleration fuel cut off----which shuts the fuel OFF on deceleration----with some mods again like cams it is necessary to turn this function OFF as the timing will bounce all over the place--especially needed if your engine is always trying to die when you lift
Another issues with cams is the idle timing will again bounce around horribly giving you an erratic idle-----To help this you can set the "minimum final timing" higher in the idle RPM areas to prevent such a swing in timing VS the commanded timing at idle
Say the final timing at idle is "0" and the commanded timing is 23* the timing will bounce around from 0 to 23
But if you make the final timing 10* then it will only bounce around from 10-23* and not 0-23* Sometimes it is necessary with very large cams to set the final timing much higher like 15* this all takes trial and error with a data logger to see what works best