Getting ready to put my Holley 670 unit on my 385 when I realize that there is no IAC unit on it. Swell. There is a casting spot for it with the appropriate "channels" to get air through, but the TPS is in the way, there is no way to physically get an IAC in there. It has the idle stop screw dealie however. Can I use this or am I boned? I mean if the engine idle is adjustable, that should be good right? Right? Right?

Steve "lookin for a 454 TBI unit"

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Steve's Trans Am Temple

 

If you plan on using a 8746 ecm then you need the IAC. The IAC is so important for an idle and TBI. The ecm uses the IAC to help keep it from stalling at stop lights, increase rpm to propertly warm up engine, increase rpm if voltage drop detected, the list goes on. Why didn't the holley come with a IAC?

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, Jon (350 TBI!)
91 Red My website

 

Well, I'm currently using a '747 but will be switching to a Haltech later. I have no idea why it wasn't drilled for an IAC, it may be one of those that comes with it's own brain box/fast idle solenoid.

It's got an idle adjust screw that opens the blades just like on a carb - why wouldn't that work? I mean, you come to a stop light, it would return to the screw stop and idle... Now the others' I don't know - how do carbs adjust for that kind of thing?

Anyone got a 454 TBI handy?

Steve

 

Steve,
I'm not running the IAC on mine right now... It was causing some idle problems. I'm also running the 747 ECM and you can disconnect it but you loose some EFI functionality.

It looks like you got the analog version of Holleys TBI unit. The digital versions use the IAC, analog units are not machined for them.


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1988 T/A,
9" Ford, 3.50 gears, Auburn posi, 700r4 -w- 2100 converter, 360ci, 9.8:1 cr,
AFR 195 Heads, Weiand #7525 intake, Lunati roller 219/227, .479/.480, 112 LSA
Holley 700cfm 4bbl on TBI truck 7747 computer and chip by Howell-EFI

 

Weird, I didn't think you could run without the IAC or you'd have some problems with idle quality. I know you can run without it because that's what you do when you're trying to get the IAC calibrated but I didn't think you could drive around without one. I know that the IAC also moves in and out when you accelorate so I don't know how the ecm would like that. Pick up a holley 670 unit for $320 and sell the one you have for $150 on e-bay.

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, Jon (350 TBI!)
91 Red My website

 

<sigh> Story of my life. Thanks Dan - Does yours throw any codes or anything? What kind of "functionality" are we talking about? If it ain't something I'll have to deal with everytime I get in the car, that ain't no biggie. No problems running, eh? I may just run this to see if it works; I can always do like Jon says and do the Ebay gig if I have to.

Thanks again,

Steve

 

You loose the IAC offset for park / neutral, IAC position vs coolant temp, and the ECM's ability to correct to a target idle speed. There may be other things as well that I don't know of.

I raised the idle speed a bit to get an acceptable idle speed in gear.

Mine does not throw any codes.

 

Are you still going to do the dual TBI thing? If so, I think the guys that do that only run one IAC. IOW, you might want to hold on to that analog unit.

 

i know of a company selling ecu's that have been reworked to push 4 injectors.

if interested, email me.