Iac

Topic: Iac (Read 4642 times) previous topic - next topic

Iac

February 16, 2005, 05:32:58 PM

Ok, real quick question. I suspect the IAC on my 3.8 is no good. I had the car running and unplugged it, and the rpms stayed at 850. Does this mean that the IAC is bad?

Re: Iac

Reply #1 – February 16, 2005, 07:39:25 PM

No not necessarily, does it raise up and then drop back down when you plug it back in?
If so then it should be fine.
What's the problem your having?

Re: Iac

Reply #2 – February 16, 2005, 08:21:53 PM

All fords put out codes, even if your check engine light doesn't come on. If you pull the codes, start with the main one. The idle is probably being affected by something else. Most IAC's can be bench tested if you take it off.

Re: Iac

Reply #3 – February 16, 2005, 10:00:06 PM

The only code it is putting out is 31, and that is for EGR valve position sensor. When I unplug the IAC and then plug it back in nothing happens. It runs exactly the same if it is plugged in or not plugged in. I am pretty sure it is bad but not positive. Also how do you bench test it?

Re: Iac

Reply #4 – February 17, 2005, 12:03:15 AM

Take not of your throttle stop position and adjust it then unplug the iac... but before that.. when you start your car up for the first time in the morning does it idle higher then progressivly idle down?

Re: Iac

Reply #5 – February 17, 2005, 12:07:31 AM

No, it always idles at around 850 in park or neutral and about 450-500 in gear. It never idles high when I first start it, it just goes pretty much to about 850. The problem that I am having is with hesitation and ignition surging. http://www.foxtbirdcougarforums.com/showthread.php?t=1595
I started this thread but no one posted anything. :dunno: It explains exactly what my car is doing.

Re: Iac

Reply #6 – February 17, 2005, 11:30:17 AM

lowcat, i'm having a similar problem as you except mine's a 5.0 Hesitation, rough idle, etc.... except when I disconnect my IAC the car stalls. not sure if it's supposed to do that or not. if you're having surging problems i think it could be your TPS. had that changed on my car and it got rid of idle surge. now it's just this rough idle and stalling...

Re: Iac

Reply #7 – February 17, 2005, 11:32:12 AM

Mine was surging,and it was the IAC AND TPS.That's my luck.I have a couple of IAC's and a TPS out in the garage.

Re: Iac

Reply #8 – February 17, 2005, 11:34:03 AM

It's not supposed to do that, you need to adjust your idle up to around 750 with the iac disconnected.
Then when you reconnect it,it should go up a bit and then settle out.

Re: Iac

Reply #9 – February 17, 2005, 12:01:36 PM

To test the IAC valve...

Get a rectangle small 9 volt battery. Then you take a wire from the battery's pos and neg... try and get the valve to move by jumpin the connecter. I'm not sure what it looks like but if there is more than one pin on the connecter just guess til it starts to move. If the valve plungers open and close then it's good, if not it's bad. you can clean them with PB blaster or something but otherwise consult your autozone person and make them test a brand new one off the shelf so you can see how it works :)

PS, it has to be a 9 volt battery... anything else shouldn't work.

Re: Iac

Reply #10 – February 17, 2005, 05:48:14 PM

Does this 3.8 have an IAC or an ISC motor?

Re: Iac

Reply #11 – February 17, 2005, 10:48:24 PM

In that picture the part on the left, with the wires coming off and the plug on the end, looks like a cylinder kinda. That is what I have. That is an IAC right?

Re: Iac

Reply #12 – February 17, 2005, 11:37:34 PM

that looks like an ISC (IDLE SPEED CONTROLL)

Re: Iac

Reply #13 – February 18, 2005, 04:10:04 AM

You have an ISC. The EEC controls the idle by controlling the ISC.
Have you ever seen the plunger move on the ISC?

When you turn off the ignition there is a five second delay before the EEC main power shuts off. During this time the EEC extends the ISC plunger to give you a fast idle the next time you start up.

Put your jumper on the self test connectors like you are going to pull codes or run the KOEO test. Turn the ignition on, don't start.
The plunger should retract all the way in. You should have 7/16" gap between the ISC plunger tip and the throttle lever. Use a 7/16" drill bit for a feeler gage.

There are four wires to the ISC. Two of them run the motor that drives the plunger in and out. The other two are the idle tracking switch. When the throttle lever presses on the plunger tip it makes the switch. This tells the EEC that it is in control of the throttle.

Re: Iac

Reply #14 – February 18, 2005, 11:17:14 AM

Yes the plunger moves. So this part is most likely not causing the hesitation and ignition surging? I've eliminated spark plugs, plug wires, and ignition coil as the cause. The only things left on the coolcats site about ignition surging are TPS and TFI. I checked the TPS and the voltage increased smoothly, and it doesn't sound like the TFI is the problem because I don't have any stalling or not starting problems. Any ideas?