Question about IAC


New Member
Apr 13, 2010
I'm working on a buddies 5.0 HO (1990). his mustang has 200k miles on it and while I was removing his IAC the bottom portion of the valve (the metal flange) broke off. I have a replacement coming soon and I wanted to try and start her up since I'm waiting for it to come in. I double checked the ignition wires to find that some of them where in the wrong spot (after fixing this) I begin to try and start the engine. (IAC is disconnected) as soon as it starts the engine dies. I even tried giving it alittle gas. Now I did a search and found this thread:

With that being said..... Will the lose of the IAC (Not connected to the harness and NOT connected to the throttle body) cause the engine to start and then die??? I understand the workings of the IAC but there is still a hole where the valve is which would allow air to enter. Also when I step on the gas the throttle plate is open so this should also allow air to enter. The only thing I could think of is programming. Someone please let me know I know engines just haven't worked on alot of Stangs. again:

1990 302 Mustang GT 5.0 HO

Thanks again

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no doubt man,its not gonna run without the iac will however run if the iac is bolted up but not plugged in to the wiring harness.not having it installed with that large of a hole showing would be a HUGE vacuum leak. definately install it and it'll run even unplugged. firing order is 1,3,7,2,6,5,4,8.plugs go from pass side front to back 1-4 and driver side front to back 5-8.if youre standing in front of the car lookin towards the engine,the second dist cap post on left hand side right past the metal holddown mechanism is where the number 1 plug wire goes and you install the wires counterclockwise starting from there.didnt know if you needed help with the plug situation or not but you mentioned something earlier about wires not bein in the right spot so figured i would tell you how to do it just in case.if you already knew how to do this than ignore my stupidity.peace man and good luck
new problems help

I got her to start.... I'm having a huge problem now. idle is at 800 rpm with .90 volts at the TPS. I made a video and I really need some help with this one. please if anyone has any ideas this is what I got:

Also heres what i've done so far

Replaced valve cover gaskets
Replaced Upper intake mani gasket
replaced the TB gasket
Replaced Fuel filter
Fixed the ignition wires (the order was off)
cleaned the MAF sensor
the IAB is new same with the gasket.
Fixed a few vacuum hose's
cleaned the TB

Also the first time I got it to start before it even warmed up all the way (while it's back firing) the CAT started smoking after a while! I shut it off after a bit. Could this be due to a bad O2 sensor??? I haven't checked the codes yet but there isn't anything lite up atm....

also It's only happening to the Right side ONLY so it has to be a bad o2 sensor right?
Yeah, I still have backfiring issues, but not like it's doing in that video. It USED to do that pop ..pop ....pop pop... pop ..thup... pop thup. ..Replace the spark plugs. Most of that backfiring on idle like that went away when I got new plugs and wires. You may also want to dump a couple cans of Seafoam into the gas tank while there is only about 2 gallons left in the tank. Then drive it around,... find a safe place you can really get on the throttle. Drive it around a little hard for about 10 minutes (Safely). I did that and it cleaned a lot of garbage from the injectors. The engine may be running rich as well. That can easily contribute to backfiring. As for mine, it surges on a cold start. Does this for about 30 seconds then clears up. But still seems to run like crap. When I rev the engine, the RPM's don't drop right away. It goes back down slowly. When I'm driving it (AOD tranny) , I'll be in Drive (not OD) going about 55 MPH. I'll step on it till it gets to about 60 MPH then I'll completely let off the gas. After a couple seconds it starts backfiring like nuts while the engine slows the car down to a lower speed... iI just noticed that tonight. And it's annoyingly loud.... sounds like POP pa pa POP POP thup thup POP pa POP. Real fast backfiring. As soon as I put my foot on the pedal, it stop backfiring. Only codes I have are 44 and 94.

And oh yeah, scan for codes. Do both KOEO and KOER codes because there will be different codes for each position. And by the way, it looks like there is an airbag code 51. That's my guess. Most of the time it is (if it is 5 blinks then 1). It's a short to ground issue. I think the problem is in the dignostic module.
So im thinking about something..... Now I noticed and was thinking about the O2 sensor thing.... I'm not sure if that's it at all now. I've been thinking about how the car runs and I noticed it back fires only every like second or 2. if it was running rich due to a bad O2 sensor then I would get a check light and it would be NON-STOP right? So i'm thinking it has to be one of the spark plugs not firing right and burning the fuel in the cylinder, then escapes and burns in the Cat (like it should) Does this sound right to you guys??? with the rate that it back fires it's consistant and not ALL the time so i'm going to find out tomorrow. let me know what you think about this.