Wicked94Z

iTrader: (26)

I realize IAC counts would probably help here, I'll get some up in the next few days. Basically I've got a big HR on a 107lsa and my car does not want to hold an idle. I've tried leaning it out, richening it up, adding timing, taking out timing, etc. But basically the same result, car will maybe hold an 1100 rpm idle when i start it up hot, if i don't touch anything it will idle for several minutes like this. But the second I touch the throttle it will want to die. I have to hold my foot on the gas while driving around, coasting, or sitting at a light to keep the thing running. I did drill a 1/16" hole in the tb and that seemed to help a bit. I guess we'll see when the IAC counts come in. I would like the thing to idle like 950 or so, which might not happen because of the size of the cam, but 1100 has very little lope and the thing is loud as **** idling that high. any help...... thanks

moehorsepower

iTrader: (3)

Please post more info, Size of cam ,Duration, what intake, injectors ect. then maybe we can help you out...

Wicked94Z

iTrader: (26)

24x/25x @ .050 .620ish lift

ported lt4 intake

bbk 58mm tb

42# SVOs

moehorsepower

iTrader: (3)

OK, Have you checked the little things, Vacum leaks, TPS voltage and percentage of throttle opening? Fuel pressure ect..

AChotrod

iTrader: (17)

My cam is no where near as big as your but we had to drill one of the TB blades out a bit and epoxied the other shut, to get a good idle.
Ill find you a pic

moehorsepower

iTrader: (3)

I was running a 244 cam 612 lift, No drill in the T/B. get it to idle without worrying about your counts. Mine were close but it idled fine both at start up and after running around...

C_Rules

iTrader: (7)

hey moe thats a pretty nice sized cam. what tables did you adjust to get it to idle fine?

is your car an a/c car. if so what would you have to change to get it to idle steady with the a/c on?

Wicked94Z

iTrader: (26)

there's an iac adj for a/c anticipate table in tunercat for that i believe

Wicked94Z

iTrader: (26)

i should also mention this is a SD OL tune, i have a wideband on order from jegs, should be here wednesday. havent really checked for vacuum leaks however since its SD it shouldnt matter quite as much as a MAF tune. i actually think it idled alot better with the brake booster hose unhooked while i was adjusting the rockers. fuel pressure is fine (stock) at idle and driving around. im thinking its just not getting enough air, because the idle never goes higher than 1100 even after dying which tells me the IAC is maxed out. moe how much timing are you running at idle? i have 38 degrees right now, maybe i need more? this cam has a lot of overlap.

duh

iTrader: (16)

Vacuum leaks will ruin an SD tune, just as much as an MAF tune....Both rely heavily on what is going into the motor. The MAF actually "reads" airflow, where SD works on vacuum telling the ECM how much of a load is on the engine. Leaks will ruin everything on an SD tune. Part of the problem is with that much overlap you're not sending much of a signal to the MAP sensor.... The more you lower the idle, the less of a vacuum signal you're going to send. I've dealt with race cars that idle at 1200 otherwise they don't stay running, now granted that is carbed, but both rely heavily on a vacuum signal, weather in the carb, or going to the ECM.....Check to make sure there are no leaks, then go from there.

moehorsepower

iTrader: (3)

I was only running about 26-28 at idle..38 might be a bit much..

JAKEJR

I had a similar problem when I installed a new HR cam in my son's 96 LT1 several weeks ago. His new cam was ground on 109 LSA and was the cause of the idle problem, since the cam's duration was a lot shorter than yours.

I cured it by enlarging the idle air hole (LOWER CENTER) of his throttle body and modifying the TPS be elongating the mounting holes then adjusting it to .67 I increased the hole size in 1/16" increments. My hole ended up a .250", but I was working on a stock TB. What would work best for you may be slightly different.

I didn't drill the butterflies at all; only the center idle air bleed hole.

I took me several attempts to find the correct size hole (correct for his engine), but since removing and re-installing the TB is pretty easy it wasn't all that difficult.

Now it starts and idles at 850 RPM.

Jake

West Point ROCKS! Nation's TOP COLLEGE per FORBES Magazine!

BALLSS

My $02 is you really need to confirm your IAC and TPS counts are on spec. I would bet $ they are not and any tuning attempts will be contaminated with incorrect IAC and TPS.

You will need a scan tool to measure IAC (tuning software can also read it). The TPS can be measured by volt/ohm meter or scan tool

TPS wants to be .67 vdc closed and 4.5 vdc full open

IAC counts want to be 32 (30-35) at idle engine at operating temp NO accessories on like AC.

With your 58 mm TB you want to drill a 1/8" hole where the stock hole would be on stock TB. Measure IAC (they will most likely be to high still) and then drill 1/64" bigger and test again. TAKE BABY STEPS 1/64" MAKES A HUGE DIFFERENCE. You may wind up with 11/64-13/64" hole.

NOW start your tune. Your need IAC, TPS and FP in spec before tuning or you will be wasteing your time. I suspect idle can be 875-900 RPM's with that cam...

ss.slp.ls1

iTrader: (36)

^^^Beat me to it.

^^^Good info there. Leaned something new.

Wicked94Z

iTrader: (26)

awesome thanks for the help guys. im going on a trip for about 3 weeks, so sorting this out will have to wait. ill update when i get home.

Wicked94Z

iTrader: (26)

just wanted to follow up on this. i pulled the timing back to 34 degrees, wideband was showing 12:1 so i leaned it out to 14:1 and now it idles like a champ at 950 thanks everyone for the input