Idle Tuning Help Needed

[VortechC5]

I have finally started working on my tune. I have been running on a tune that was originally done when I installed my first supercharger using stock heads and cam.

My current setup is a different supercharger (Vortech T-Trim) running about 1psi more boost, AFR 205 heads, and a Comp 220/224 .581/.581 115+2 cam with XER lobes. The car is a 2002 Corvette with a 6-speed and I am doing my tuning at an altitude of 7000 feet.

Before I first fired the car after the latest mods I upped the idle to 850 hoping that it would idle. It actually idles quite nice at that speed except that when I let off the throttle and let it return to idle the RPMS will sometimes drop to 500ish, recover, and then it will idle fine. I have no surging, it never stalls, and I have no cold start problems.

I did a bunch of reading on this forum. LS1Tuning, and LS1Tech to see what I should try to cure the problem. I tried the (nogo suggestions) VE 60/70/90 change, IAC Park Position 40C up to 21, Idle Air In Gear all points 60c up to 8.6. These changes induced surging, stalling, and hesitation so I put everything back to stock except the idle which I left at 850.

Does anyone have any ideas on what to try to get rid of the idle dropping (but never stalling or surging) and then recovering?

Thanks,
Mark Forbes

[JohnL]

What are your "throttle follower" settings?

John

[VortechC5]

Here are all of my Throttle Follower settings. They are stock 02 Corvette.

LABELS Throttle Follower Aiflow
% Value
0.00 0.000000
0.51 0.000000
1.02 0.000000
1.52 0.395281
2.03 0.790562
2.54 2.379436
3.05 3.968310
3.55 4.603860
13.55 9.517744
23.55 15.795734
33.55 15.795734
43.55 15.795734
53.55 15.795734
63.55 15.795734
73.55 15.795734
83.55 15.795734
93.55 15.795734

LABELS Thottle Follower RPM
RPM Value
0 7.936620
400 7.936620
800 7.936620
1200 7.936620
1600 7.936620
2000 7.936620
2400 7.936620
2800 7.936620
3200 7.936620
3600 7.936620
4000 7.936620
4400 7.936620
4800 7.936620
5200 7.936620
5600 7.936620
6000 7.936620
6400 7.936620
6800 7.936620
7200 7.936620
7600 7.936620
8000 7.936620

LABELS Gear
MPH First Second Third Fourth
0 0.201516 0.201516 0.201516 0.201516
2 0.317775 0.317775 0.317775 0.317775
4 0.472787 0.472787 0.472787 0.635550
6 0.635550 0.635550 0.635550 0.953324
8 0.953324 0.953324 0.953324 1.271099
10 0.953324 0.953324 0.953324 1.588874
14 0.953324 0.953324 0.953324 1.906649
18 0.953324 0.953324 0.953324 2.379436
22 0.953324 0.953324 0.953324 3.177748
26 0.953324 0.953324 0.953324 3.177748
30 0.953324 0.953324 0.953324 3.177748
34 0.953324 0.953324 0.953324 3.177748
42 0.953324 0.953324 0.953324 3.177748
50 0.953324 0.953324 0.953324 3.177748
58 0.953324 0.953324 0.953324 3.177748
66 0.953324 0.953324 0.953324 3.177748
74 0.953324 0.953324 0.953324 3.177748
82 0.953324 0.953324 0.953324 3.177748

LABELS Throttle Follower Decay Delay in Gear
MPH Value
0 0.000000
2 0.000000
4 0.000000
6 0.000000
8 0.000000
10 0.000000
14 0.000000
18 0.000000
22 0.000000
26 0.000000
30 0.000000
34 0.000000
42 0.000000
50 0.000000
58 0.000000
66 0.000000
74 0.000000
82 0.000000

LABELS Throttle Follower Decay Rate in P/N
MPH Value
0 0.046504
2 0.062005
4 0.077506
6 0.317775
8 0.790562
10 2.379436
14 6.347746
18 7.936620
22 7.936620
26 7.936620
30 7.936620
34 7.936620
42 7.936620
50 7.936620
58 7.936620
66 7.936620
74 7.936620
82 7.936620

LABELS Throttle Follower Decay Delay in P/N
MPH Value
0 0.000000
2 0.000000
4 0.000000
6 0.000000
8 0.000000
10 0.000000
14 0.000000
18 0.000000
22 0.000000
26 0.000000
30 0.000000
34 0.000000
42 0.000000
50 0.000000
58 0.000000
66 0.000000
74 0.000000
82 0.000000

[wait4me]

looks like you just need to open up your throttle blade a little more,

[JohnL]

Maybe it's the decay rate that you want to change, at low MPH. Does the stalling happen when you're driving, or stopped?

John

[VortechC5]

Can I do that on a Vette? Ithas no adjustment screw like some other vehicles.


looks like you just need to open up your throttle blade a little more,

[VortechC5]

It usually does it when I push the clutch in as I am slowly rolling up to a stop. It doesn't actually stall the idle just drops to 500-600. The idle is set to 850.

Would I increase the decay rate?



Maybe it's the decay rate that you want to change, at low MPH. Does the stalling happen when you're driving, or stopped?

John

[curtbriggs]

In Tune, Engine calibrations, Idle, double click on "Desired Idle Speed", there are four columns under Conditions, labeled:
In-Gear A/C on, In-Gear A/C Off. In P/N A/C On, In P/N A/C Off.
Note: The scale on the left is engine coolant temperature, not outside air temp.

I had set the idle speed in the two on the left, and when rolling with the clutch in, the idle dropped back to a rolling low setting. Set the idle speed in all four columns for the engine operating temperature range. I started at 1000 RPM for a cold engine and went to my desired 910 RPM for normal operating temperatures for my 160* TStat. I would set the normal speed 10-20 RPM high in the two right columns for the manual transmission.

Note: An easier, faster way is to use the two graphs above the four columns, right click and drag the cursor to the new idle speeds curve that you desire. Do both graphs. Double check for the correct idle speed for your normal operating temperature in the four columns below and adjust if necessary.

This worked for me.

Cheers, Curt
_____________

[jfpilla]

It usually does it when I push the clutch in as I am slowly rolling up to a stop. It doesn't actually stall the idle just drops to 500-600. The idle is set to 850.

Would I increase the decay rate?



Maybe it's the decay rate that you want to change, at low MPH. Does the stalling happen when you're driving, or stopped?

John

When the car is rolling or coming to a stop it is not in idle mode. The likely table to adjust for starters is the idle airflow table(it should really be running airflow). Watch the ECT where the transition to idle overshots the desired rpms and increase the values, by ECT, .01 at a time.

[VortechC5]

Thanks for the help guys. Now I have some stuff to try. I'll report back when it is solved.

[curtbriggs]

Mark, if you follow my instructions as I prescribed on your thread and it will fix your problem.
My farm has a 1 1/2 mile gravel drive way, half of which comes off a 700 foot ridge line. I idle down in neutral, 6 speed, to pick my way around the rough stuff. My 950 RPM stable idle (using only the first two columns) would drop to an unstable 750 to 950 RPM. Changing "ALL FOUR" columns, the last two of which appear to be for an automatic transmission, but are also for the manual gear box, corrected this back to a stable 950 RPM idle.

Cheers, Curt