New Combination New Problems

[Mean LT1]

Heres a little info on the bullet:

94 camaro Z28
355ci
AI 215 triflow heads milled 58cc
242-248/580-585 110LSA
JE -5cc flattop pistons
11.0-11.5 static comp
stock intake
58mm t/b
long Tubes
Borla Exhaust

I just got this build running and im having the toughest time getting this motor to idle correctly. I understand its big cam for the cubes but the compression and heads will make it scream...hopefully. Im using TunerCat/Datamaster 3.4.1. My commanded idle cold is 1200 and hot at 1000rpm. Timing is at 28 degrees. I am having trouble getting the IAC to help the idle. Right now its pegged at 160 and will not move. The only way to start the car right now is to give it a little gas and it will fire up but will not hold an idle. So...what I got from this was to open the blades and unplug the iac. I figured i would get the car running without the iac and when I have the idle set where I want, then plug the iac in.

So I get the car started which fired up right away with the blades opened up and it idled at about 1500. I closed the blades up until I reached about 1100-1000 rpms. tunred off the car, plug back in the iac and verified the iac was now at 0. Started the car back up and then it wanted to idle at like 400-500 rpms.While it was trying to idle the counts were increasing all the way back to 160 where it eventually died.

It really doesnt matter if its open loop or closed loop, it does the same thing. Now Every now and then it will act like it has sense, and will idle but the iac is not helping at all. One last thing...if it is actually maintaining a decent idle, if the fans come on it will immdietly drop down to 400-500 rpms until they shut off.


So if you've read all that and still willing to help I would appreciate it. I have datamaster logs and very familiar with Tunercat.

TIA

Shawn

[steveo]

it needs more air.

your aftermarket throttle body may not have an idle air bypass hole, or it is too small.

cracking the blades open and disabling the iac isn't going to do you much good, the high tps voltage will screw with things, fooling the ecm into thinking you're holding the throttle open, especially if you do not unhook the battery after so it can reset to zero.

this type of intake plenum has special idle air passages for more even air delivery at idle, which moving air past the throttle plates will negate. this is why you dont 'set the idle where you want it' with the plates.

i reccommend you close your throttle blades almost all of the way, and then enlarge the idle bypass hole bit by bit until your hot IAC counts are about 60 or so.

[Mean LT1]

it needs more air.

your aftermarket throttle body may not have an idle air bypass hole, or it is too small.

I have a Holley 58mm t/b. Actually the iac hole is quite large. Ive never heard of any problems with this t/b. I will drill it out bi t by bit like you suggested. I feel as though it shouldnt need alot as it does not require very much throttle to get it started. I will keep you updated.

[Mean LT1]

Update

So I decided to swap out my Holley t/b with a spare Professinal Products peice. The IAC hole for the holley was just too much of an odd shape where as the PP was circular. So I took a drimmel and opened it up some some until I saw the IAC start to move from 160. It took three tries to get it moving in the right direction. Right now its sitting at 95-100 hot idle which is cool bc at least its holding my idle at my commanded rpm. I know I need to enlarge it a littl more to bring it down but just thought I would share the news.

[steveo]

glad that did it

95-100 hot idle would probably be fine, but i bet cold start will act up on you one day if you dont get it down a bit more.

a cam that large is going to play hell with closed loop too.

you can force a richer open loop idle using power enrichment



at this point just dial up more fuel and timing at it until it's stable enough and your exhaust doesn't smell awful