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?
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?
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.
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?
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?
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.
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...
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.
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.
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.
Does this 3.8 have an IAC or an ISC motor?
(http://users.rcn.com/jroyle/CFI%20ISC%20'84.gif)
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?
that looks like an ISC (IDLE SPEED CONTROLL)
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.
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 (http://www.coolcats.net/tech/troubleshooting/surge.html) 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?
The only way the ISC could cause surging would be if the plunger is moving in and out while at idle.
Try disconnecting and pluging the vacuum line to the EGR valve.
See if that makes a difference in how it runs.
Lets start over.......
Have you checked your fuel pressure..
New ideas here, Fresh thoughts!!
I am almost certain it is something to do with the ignition. But, I will check the fuel pressure. This is what the car does:
1.) Start car, car idles normal and everything seems ok
2.) Put car in gear, at first it acts normal and engine does not hesitate
3.) Driving, suddenly tack will jump around from about 1k up to 4k, this happens during acceleration, cruising, idling, it doesn't seem to matter. It seems like it occurs at random times. During the ignition surging the car hesitates/misfires.
4.) About a minute passes, the tack will go back to normal and the engine will stop hesitating/missing.
This happens at what seems random times. I drive 120 miles everyday, sometimes the engine will only do this once or twice, other times it will do it most of the 120 miles.
Seems like it to me too. Since the tach's reading is based on how many/how often ignition pulses are being sent to the coil, it sounds like there's a whole bunch of signals arriving when they shouldn't be.
Have you checked inside the distributor to make sure there's nothing bouncing around in there that interfere with the Hall Effect Sensor or its parts? I remember seeing a Tech "stumper" in the back of an auto magazine where they found the roundy-round part had actually separated from the shaft. Maybe yours just has something messing with the windows, or stuck between the sensor and magnet.
Like MasterBlaster says the Tach is driven by ignition pulses.
The problem is probably where he says it is. Something quick you could try to eliminate the EEC as a suspect is drive with the SPOUT disconnected for awhile.
Dumb question, what is the SPOUT, and where is it? When I took the distributor cap off I didn't find anything but I did notice these scratches in the plastic of the cap. I don't know if that is normal or not.
Looks like someone either spun the engine when the cap wasn't screwed down, or had no idea which way it was supposed to go on and kept twisting it back and forth until it finally popped on, scratching the insides with the rotor tip.
Spark out (SPOUT) is the wire from the EEC that tells the Thick Film Ignition (TFI) module when to pulse the ignition coil.
The TFI is mounted on the distributor. Look at the cable plugged into the TFI. One of the wires has a connector that allows you to disconnect that one wire. That is the SPOUT.
This allows the TFI to pulse the coil without control from the EEC.
Your ignition timing will stay at the "base" timing of 10 degrees BTDC.
So if I unplug this wire, and the car stops the ignition surging/hesitating the computer is bad?
It means the computer may be bad.
It takes some very sophisticated and expensive tools to pin something like this down 100 per cent for sure. Especially without a process of elimination to eliminate some of the suspects.
So the best we can do is give you some insite in how it works and
suggest what is most likely the problem.
I will say that if it still surges with the SPOUT disconnected and this is really an ignition problem, it is not the computer.
The Hall Effect mechanism in the distributor, that MasterBlaster suggested you check out, generates a pulse.
The TFI sends this pulse the PIP (profile ignition pick-up) to the EEC.
The EEC after making adjustment to timing, sends the pulse back to the TFI as a SPOUT pulse.
So take the steps suggested and post the results. Then we can buttstuffyze it further.
I fixed the problem. It was the TFI. Now it runs normal, and just in time to go through emissions which is due by tomorrow.