k-mart

iTrader: (5)

Just installed a ported FAST 90/LS2 TB and 30lbs svo's. Now the car won't idle at all. It will hang at about 900rpm (idle set to 975) then fall to about 400rpm and jump back up over 1400rpm until it finally drops completely off. I adjusted for the injectors by copying from a tune on the repository.

Is there a general baseline that I can follow to adjust for the FAST? Any help would be greatly appreciated.

Thanks,

Kevin

PS: Before the FAST, the car idled pretty well at around 950rpm.

Frost

iTrader: (45)

Is your min airflow screw setup? What are your IAC counts at hot idle (if not steady, what is the upper and lower range that they are seeing)?

Frost

iTrader: (45)

Here is an excellent injector spreadsheet that Doug Stalter posted over on HPTuner's forum that can help you get your IFR straight if it isn't already.

k-mart

iTrader: (5)

What is the min airflow screw? I assume it is on the TB itself? If so, does the LS2 TB have this? If you can't tell, I'm a tuning newb. Thanks for all of your help.

As for the IFR, the tune I'm using has them set at 0 = 4.5547 up to 80 = 4.984 gruadually increasing as it goes up. That spreadsheet says I need to drop by about 0.2 across the board. Would that make a big difference?

Thanks again,

Kevin

Cam72aro

iTrader: (28)

Idle airflow probably needs to be recalibrated.

Doc

iTrader: (9)

You don't have a idle set screw on you electronic throttlebody on your C5.

Bigger concerns would be the installation of the FAST.

Did you use the button head valley cover bolts supplied with the FAST? Did you torque the manifold to the GM torque spec in the approved squence? Many folks will attest that the GM spec is not enough. Is the MAP sensor seated tight? Iv'e had to rtv every one I have encounter as there is no provision like the LS6 to hold it in place.

A high uncommanded (read- not a misadjusted idle airflow table) idle is usually a result a leak of some sort or another.

Frost

iTrader: (45)

doh! Well that's a fairly good point Doc

k-mart

iTrader: (5)

I did use the FAST button head bolts. It doesn't seem to be an intake leak as upon cold start-up it will idle pretty well. Around 120deg., it settles down to 975rpm. Once it heats up, though it starts jumping around a bit. If I give it gas at this point it falls, stutters, jump up to about 1500rpm then dies. It also doesn't want to start when hot.

Could this be a throttle follower or cracker problem?

Thanks,

Kevin

turbolx

Have you changed the throttle area scalar to accomodate the new 90mm opening? This has a HUGE influence on idle control for ETC vehicles.

Beyond that, you can get more specific with tuning the injector offsets and short pulse adder to improve low load consistency.

Throttle cracker and RAF changes are band-aids for incomplete fundamental tuning changes in this case.

RedHardSupra

iTrader: (1)

here's a spreadsheet for adjusting the throttle area scalar:

http://www.marcintology.com/tuning/TBresizing.xls

k-mart

iTrader: (5)

I have not changed the throttle area. Hopefully this will cure what ails me. According to the chart, I should move up 133%, from .0225 to .0339. Does this sound right?

Thanks for all the help. You guys are awesome.

Kevin

edcmat-l1

iTrader: (10)

Fairly good point Steve?! ROFLMAO!!

Frost

iTrader: (45)

Yeah Doc made a fairly good point there

that's sure not the first time that I have made the F-body assumption (or missed a sig) to be honest and likely won't be the last.


k-mart, did you try that out?

k-mart

iTrader: (5)

Won't get a chance to try it out till tomorrow. Don't wanna bother the neighbors right now.

I'll let you guys know tomorrow evening.

Thanks,

Kevin

k-mart

iTrader: (5)

That helped a lot guys. I've at least got her idling fairly well once it settles in. The only problem now is coming off the throttle it wants to drop down to about 700rpm then jump back up near 1100rpm. After it does that, though, it settles down pretty good.

Any ideas?

Thanks for all the help!

Kevin

Doc

iTrader: (9)

Attention "Kmart" shoppers, uncontrolled airflow clean-up on aisle ten!

Sorry, I couldn't help it.

Welcome to the wonderful world of controlling the pitch of the throttlebody blade (in your case,)(with a cable driven Throttlebody, the IAC valve) via the aftermarket software suite of your choice.

A hint- (Assuming fueling and spark are inline) Throttle Cracker.

Delicate stuff here kiddies....easy to miss when you are merely observing and not participating- Realtime tuning is your best LSx education path.

Both the Major LSx based "religions" offer this sacrement- in very different ways though.

You be the judge.