Help With Bad Idle

[86LT1MCSS]

I am trying to get the idle right on a 99 camaro with a T-rex cam (242/248 - .608/.612 - 110 lsa)and 37# Delphi/Lucas injectors before they go to the IHRA bracket finals at Rockingham this Wed.The problem is that it doesn't crank up unless you have your foot on the gas a little if the engine is warm and once it starts idling fairly stable then you tap the gas the idle drops back down too far before it catches itself.The AFR on my wideband is up and down between 14.3 and 16.5 but the idle is up and down as well.
Here is the log and current tune.

Thanks

[LS1_Sounds]

I had to fix the same problem when tuning a friends TRex car. Everything was great except the initial startup. Trying making the following changes under Idle > Idle Airflow > Startup:

Startup Airflow Decay = 0.4
Startup Airflow Initial = +3 g/sec across the board
Startup Airflow Delay = 100 revs across the board

[86LT1MCSS]

Got a chance to mess with the VCM controls and it idles the best if I add 45 degrees of absolute timing and put the AFR control on 18.
What is the IAC position I should try to shoot for?
Is this cam too big for closed loop idle or do I need to turn off the fuel trims?
Which table should I try to add some timing to?
Seems as if it likes to run alot leaner than the fuel trims will let it.I noticed the fuel trims around idle are 20-25 so I added some to the MAF table and it got worse.
I also pulled a plug out and it is pretty black.
One more thing too is this car has long tubes with just some bullit mufflers.I'm not sure but does that have something to do with it?

Thanks

[EC_Tune]

Set the OL EQ Ratio table from 140 F on up to 1.0 That will help the startup a bit.

Also look at the Fuel Tab> General and look over the Afterstart Enrichment Initial Adder vs ECT. Multiply that whole table by .5 and that should help as well. That table is the equivelent of a Choke function.

That cam is too big for closed loop idle and for MAF. If you have a wideband in it, tune it in open loop SD mode. You'll be much happier and things will be much more consistent. The reversion generated by that cam is making your PCM think the car is lean and is over compensating thus the black plugs. It will also affect the MAF as the MAF doesn't know which way the air is really going and is seeing the reversion through the intake & throttle as additional airflow.

EC

[86LT1MCSS]

EC I there any way to do a open loop just on the idle?Seems like I recall some people doing that on LT1s but I dont know on the LSx.
I did a full SD tune and it did pretty good so I guess I will go back to that.Just trying to learn as much as I can about all the different ways to tune.

[EC_Tune]

You can set the PE EQ ratio to 1.0 - 0.98 in the idle range only. Then set the TPS value to 0 as well in the idle range only. That should cause the system go to into "PE" mode at idle and drop to open loop. MNR-0 has done this on a few big cammed cars as well.

EC

[86LT1MCSS]

Ok so I got my idle stable with open loop.The only thing that I have been trying to fix is if you are in gear idling and tap the gas it will cut off.
Any ideas?

Thanks

[bullygoat]

You might want to try dropping the 400 RPM column by 20-30% and adding a little bit of throttle follower air to the idle. If you watch the log you posted, your Injector PW jumps up as your RPMs drop causing it to flood the motor. You have no throttle follower for 1.5% TPS and down so the throttle blade snaps shut and the IAC motor comes down real quick and chokes the motor for air. Kind of a double edge sword.

Tim

[EC_Tune]

Check your IAC counts at idle. If they are 80+ you need a bigger hole in the throttle body. Can't tell you how big, just cut & try. Make sure you drive the car a bit between upsizes...

[Russ K]

With a T-Rex cam, you need at least 1000 rpm idle in gear, and 1050 rpm in P/N. Your idle map is ~72kpa, so your LTFT map & rpm boundaries need to be set up. The IFR table is too high for 37# injectors, causing positive LTFT's.

Put the cranking fuel tables back to stock. Then you need to get the RAF table right, I would start by adding 4 g/sec to the stock table values at all temps. Don't drill the throttle blade as that will throw off the desired airflow and STIT & LTIT relationship. What stall TC are
you using?

And get your wb to work with the scanner, it will make the VE tuning easy!

Russ Kemp

[86LT1MCSS]

Thanks everybody.I will go back and look at those areas.
One more thing to add is it will flood pretty easy on cold startups too.
On the throttle blade,I opened it up with the stop and reset the TPS.The IAC counts are around 45 now.
The converter is a 4800.