0ski_dwn_it

When I went to the single plane, there was not enough room for my T-stat and my IAC to fit under the throttle body together. As a result, I had little choice but to remove one of them. Well we all know which one went. The IAC.

I took the IAC housing off, unscrewed the sensor from it, plugged it into the harness so the computer would see it. Built a blockoff plate from some 1/8 aluminum sheet, and blocked the passages off to the TB.

I am thilled with the results the car NEVER hunts for idle, and the idle is rock steady all the way down to 600RPM. Well as rock steady as a 251/251 duration solid roller with .620 lift can be. There is definately a serious lope to it, but its not the revving , near stalling and revving that the IAC gives at times.

The IAC really serves little purpose in the grand scheme of things. Its basically a controlled vacuum leak that changes idle slightly to achieve a desired RPM. This can easily be done through the throttle blades also.

I have written many times that you want 95% of the air at idle to be going through the Throttle Body and only 5% through the IAC for a steady idle. Most of the time on mine I would set it as high as 98%-99%, this gave the car the best (smoothest idle.). I think that most of the people that have idle/stalling problems have this ratio backward, or too much air going through the IAC. Then throw a large cam like the 219 into the mix, and what you have is air surging into the engine, the IAC seeing the slight rise in RPM, it tries to correct, this ultimately causes the "windmill" effect that most complain of that ends with the car stalling.

I am not condoning that everyone run out and remove there IAC, but if I had it to do all over again, mine would have been taken off back when the 350 got the heads/cam/intake :cheers:

If your having idle/surging problems I suggest you first open the throttle blades a little via the min idle screw. Then you may want to explore the blockoff plate scenerio.

Hope this helps some of you....

:cheers: :steering: :thumbs:

scorp508

Is this driveway testing or have you actually been driving around like that for a while? I'm curious. How does the car react in a part throttle to instant 0% throttle condition on the street? You wouldn't think GM would put that on there and spend the kind of research $ they had to if it were not necessary.

AS84

interesting- i sent my single plane back to jeb because of the same issue. I wonder if an speed density car uses the IAC any more than the MAF cars......

bogus

I see what you are saying, but I have always suspected the IAC was designed to deal with emissions and drivability, more than anything else.

CFI-EFI

The IAC is great for stock or mildly modified engines. It adjusts the idle for the a/c and an auto going into drive. Mine even kicks in when the fan turns on due to the alernator draw. I'm sure it is too slow reacting to keep a loping engine at a steady idle. It goes into a death spiral. Just as it tries to speed up from the slow end of the lope, the lope speeds it it up. As it tries to control the higher idle it shuts down... Eventually, excessively. It is a great thing on a stock engine. Jessie"s discovery makes perfect sense, to me.

RACE ON!!!

93Quasar

I've never had an idle hunting or stalling problem, but I do notice that when I pull up to a stop light, it will idle at 1600 rpm and then drop to the 900 range after you sit there for a couple of seconds. Is this at all related to response time of the IAC, or totally unrelated?

Steve85

That is a good point, I believe the IAC was the most effective way to electronically control idle speed, mostly to allow a high idle on a cold engine to reduce open loop operation. On newer vehicles with fly by wire there is no IAC and idle is controlled by the the throttle plate position. Very similar to what he has effectively done here.

However, for the daily driver, there is also the need for an oem car to operate in almost any condition and adapt to varying conditions without driver adjustment. My guess is we could get away without the IAC 90% of the time. That is to say, you would probably have to adjust your idle screw incrementally throughout the seasons to maintain a consistent idle quality.

scorp508

Yep, forgot about that one. In the winter up north here that is a godsend having the multiple idles in reference to coolant temp.

ericcer

Very interesting discussion. I have had idle and cruising issues for a year and a half with no cure. Sounds easy enough to try out.

What if I plugged the little IAC hole in the throttle body? Wouldn't that kill the air supply to the IAC? Wouldn't that do the same thing? Maybe there is a way to kill it with LT1 Edit too.


[Modified by ericcer, 4:15 PM 5/7/2004]

Upstate

Now to me that is very interesting. I have a pretty mis matched combo of Jebs single plane /stock 113s/ and a 219. Granted I think my car has other issues but i get the same wind mill effect, but only during open loop. Once I go closed loop my idle is great but have the same issue as mentioned above about coming to a stop; have a high idle that slowly winds back down.

I am slowly learning about what the ECM is doing and as I understand it WOT = open loop, open loop= my car runs very badly.

My last time out at the track was an embarassing event. Major bog at WOT w/ 60' times in the 2.4 to 2.7 range, and I could hear the IAC whistling as I was going down the track, netting a worst for the day 15.1 at like 94 MPH.

Which reminds me, Jesse, I am sorry for not getting back to you sooner about burning a chip. The price of admission for EASE is a little steep. I downloaded WinALDL and made the cable, and d/l' ed panalyze but I haven't done much logging.

About the only thing I remeber from just hooking it up were that my IAC counts were 0, and my BLM's were at 160, during closed loop. I plan on trying to get some good logs this weekend and hopefully you'll find the data usefull.

0ski_dwn_it

Ok let me try to answer a few of the questions/comments here.

Scorp. YES the car has been driven now for the past month or so, in 80+ degree weather and also our wonderful Northern PA weather, which has been below 30 degrees. The car idle perfect in all situation. Warm motor or cold. Its actually as I described steadier than ever before.

Ok now your next question. Throttle response, I can imagine any more throttle response than this thing has. Put it this way, if you were in the passenger seat, and I told you i was going to bounce your head off the head rest, trust me, you could stop me from doing it. With a simple blip of the throttle. ;)

Now to hitting the gas very sharply off idle and letting it fall. This is exactly where the NO IAC shines. Since all the air needed for idle is coming through the throttle blades, idle is returned and maintained perfectly.

And I'm sure that GM did invest some time into the IAC developement. But is your car running the Air pump? I'm sure there was time invested into that as well. But we all know the cars run fine without it.

IAC is not a problem on stock cars since the cams are little peanut lobes that don't effect the signiture pattern of the plenum/incoming air. Put something bigger in there and listen to it hunt for a constant idle.

Another great thing about the IAC delete is after the battery is disconnected there is no more hunting to find the desired idle.

Lets all stop and think for a second. How does a carb work with respect to air flow? The same as our throttle bodies.

Its my opinion, that its the best thing I have done in terms of getting a consistant smooth idle and fighting off stalls in situation etc.

As I said its something that should be experiemented with. I don't think its needed for everyone. But I certainly would not spend money on replacing one once it goes after having experienced going without it. And I certainly would not live with erratic idles/stalls if this would cure it.

Its not needed for anything important. One thing it does, and this has to be one of the stupidist things I have seen is: On an automatic, going from reverse to drive you have to pass through neutral. In the chip, the idle is raised 50rpm when the neutral switch is made, this is done by the IAC opening slightly. What this does is rev the motor, so when you put it in gear it slams, rather than just maintaining the park desired idle and going into gear smoothly. In every chip I do, its one of the first things I remove from the stock configuration. Its not needed and counter productive in my opinion.

But its one of the important controls the IAC performs :lol: :jester


[Modified by ski_dwn_it, 1:30 PM 5/7/2004]

Steve85

".... in 80+ degree weather and also our wonderful Northern PA weather, which has been below 30 degrees. The car idle perfect in all situation. Warm motor or cold. Its actually as I described steadier than ever before."

That's good news, at least 75% of the time when I first start up, come to a red light/stop sign, or as I pull into the neighborhood my car sits at 1500 and very slowly works down. Very annoying, it sounds like I'm holding the throttle open to show off or some shat.

See below for can of worms
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SIDEBAR: There was much ado about this manifold being a direct bolt-on. Did I miss something with regard to these necessary mods? Keep in mind the manifold has been feverishly defended on this premise (as well as performance) numerous times. And don't go reading a bunch of crap into the statement/question, there is no opinion or claim made.

65Z01

I believe you are right about the IAC delete working well on a modded engine if hunting idle were a problem.

But remember that a carb engine works much like the new fly-by-wire EFIs, i.e. it uses the throttle plates to achieve a fast idle in cold weather. I think this is the only feature missing by deleting the IAC.

I would bet that the IAC is at least in part used for emission control too.

Anyway, this is a very interesting post; and brings to light something I hadn't considered. :cheers:

0ski_dwn_it

[QUOTE.

SIDEBAR: There was much ado about this manifold being a direct bolt-on. Did I miss something with regard to these necessary mods? Keep in mind the manifold has been feverishly defended on this premise (as well as performance) numerous times. And don't go reading a bunch of crap into the statement/question, there is no opinion or claim made.

[/QUOTE]

Jeb has a T-stat that he has that will work. I used that one when I ran the setup last year. We/He forgot to send one along with mine, and instead of bugging him I just took one to the local fab shop and had them fix it. He also sent a modified IAC housing with the intakes. So as a package it was able to use the IAC.

But this is something that has been on my mind for a while and gave me an excuse to try it. Thus far I have to say I don't miss the IAC for one second.

Also as with most all my testing of stuff, I usually put it through its paces before I say its good or bad. Therefore there is some backbone to it.:yesnod:

If it sucked without the IAC, you know in a second it would be back on the car. :cheers:


[Modified by ski_dwn_it, 2:26 PM 5/7/2004]

Steve85

That works for me. My MR from TPIS is "bolt-on" and required more mods than the SP manifold you have there. Was just a bit surprised and curious.

Glad you tried w/out the IAC, it's worth a shot for many of us with a little extra lope in our Cheerios. :cheers:

Upstate

Just some things others should be wary about while the install is still fresh in my mind, that I haven't seen mentioned on the forum. Some of the items below are in the instructions Jeb provided.

You have to cut out a portion of the accel/cruise cable bracket to fit over the fuel rail.

Intake will not fit 113's as is. Modifications must be made to either the head or the intake. I opted to grind out a recess in the lip of the less expensive cylinder head than to take a chance grinding on that intake and screwing it up.

The coolant passage under a stock TB will have to be completely cut away, and some of the screws ground flat. The vacuum port under the TB also needed to be cut down a bit.

My only gripe is it is not possible to reach the min idle screw without removing the TB. The plenum covers the hole about half way but it's nothing a little grinding won't take care of.

I have nothing bad to say about the intake, or Jeb, and am a satisfied customer. Just need to log some data and get a chip burned.

I have had nothing but problems with the IAC and I will certainly check out what removing it does. Seems logical enough.

0ski_dwn_it

Upstate:

Your right there are some minor things that need massaged, but if you think your going to buy anything performance related that is as major of a undertaking as making a new intake, your in the wrong hobby. Jebs intake did have a few corks, but I had mine installed within 1 hours of actually trying to put the intake on. And I have taken it off 3 times since the startup 3 weeks ago for various checks of items, etc. I can tell you that is comes off in about 20 minutes and goes back on in 30 minutes. It takes longer to clean all the surfaces than it does to take it off and re-install it. :lol:

The SR was an awesome manifold. But if I had to take that off 3 times in 3 weeks. I would NOT be a happy camper. :lol:

Small tweaks on performace equipment is expect from ANY vendor. Hell I bought a melling 55HV pump for the 434 and it did not even come close to fitting the dowel pins. Had to hone the through holes a bit before it would drop down on the dowel. As I said, when dealing with different vendors and different makes/models - your guess is as good as mine with what will fit and won't.

The intake for me was much simpler despite the few small corks than the SR ever was. And believe me I loved that intake and still do. It just can't compare to this single plane.

As for the IAC, its something to keep in your back pocket should the time come when you need to smooth out that idle.

85vet

Jesse,
If you recall, my car ran w/o the iac last year. The only problem I saw and had was with nthe A/C. If you want to use the A/C on the highway only, then the elimination of iac is fine. But if you want the iac for city driving - forget it. The car will die at stop lights.
Remember that you eliminated your A/C.
Jim

0ski_dwn_it

Jim.

No I did not know you had it removed. The IAC, yes controls the idle for the AC when its kicked on. But it only adds a minimal RPM. You should have been able to raise the base idle slightly to compensate and keep the car running. My bet is if you do that, it will idle fine with or without the AC on.

:cheers:

85vet

Ski,
I did try adjusting - the idle would be tooooooo high normally to allow the A/C to kick on. At least on the 85 it sucked big time. I did go back with an IAC for this reason only.
Jim