Quick IAC question... I think.

Topic: Quick IAC question... I think. (Read 2557 times) previous topic - next topic

Quick IAC question... I think.

March 07, 2005, 06:43:11 PM

I got the sneaking suspicion the iac is on it's way out. It's idling high than normal (only about 200 more rpm) when it's in drive. When it's in park, it's typically running around 1000 to 1200rpm. Ocasionally I get surging when it's in park or when i'm driving, i've hit nearly the 3k mark in park and typically no more than 1k in drive. So just wondering if the proper testing technique is to unplug it while it's in park and running, and if it surges and then calms down and stays down it's fine? I'd assume that if it keeps surging up and down it's bad? Just my guess, but i'll let the pro's correct me!

Re: Quick IAC question... I think.

Reply #1 – March 07, 2005, 08:23:05 PM

I think I had the same problem as you. The tack will jump around once in a while and when that happens it runs like . My problem turned out to be the TFI was on the way out. But from what I have gathered to test the IAC you have the car idling, while idling unplug the IAC and the RPM's shoud drop way down. If it does this I believe the IAC is ok. I might be wrong thought.

Re: Quick IAC question... I think.

Reply #2 – March 07, 2005, 08:27:53 PM

K, well, the the rpm's don't drop. I hope the tfi isn't going, kinda would put a kink in my upgrade plans.

Re: Quick IAC question... I think.

Reply #3 – March 08, 2005, 07:03:35 AM

Sounds more like your TPS...Found this on google by typing in "Adjusting TPS voltage Ford 5.0"

Quote

A common problem in the EEC-IV controlled 302 Mustangs is a hunting idle. This is an idle which fluctuates in RPM up and down and up and down....It can be very annoying.

There are a lot of tricks people use to try to fix this problem. Most of them don't work.

One common trick (that doesn't work) is to try to "fool" the EEC-IV into thinking the engine is still in warm-up. This is accomplished by installing a low temp thermostat and/or removing the ECT (engine coolant temperature) sensor. It fails when the HEGO sensors detect a too rich fuel mixture, and the EEC-IV compensates by leaning the mixture out. Now you're back to the hunting idle.

The EEC-IV is programmed to idle the car at 672 RPM. Incorrect throttle plate position is ithe primary cause of the problem in most cars. To adjust this, back the screw out until it no longer touches the throttle plate stop. Insert a 0.010 feeler gauge between the screw and the stop and turn the screw until it touches the feeler gauge. Then turn the screw another 1.5 turns. Then adjust the TPS (throttle position sensor) to 0.98V.

Re: Quick IAC question... I think.

Reply #4 – March 08, 2005, 09:49:11 AM

I agree with Pauley, most fast/hanging idle problems are due to the TPS.

If you unplug the IAC and it still idles high, then likely it has a vaccum leak(if you haven't been trying to adjust the idle). IF it drops and idles slowly (or stalls), then its probably the TPS. At that point you should check to see if there is less than 1v on the green wire(should be .7-.95). If its over 1v then it will idle high...

Re: Quick IAC question... I think.

Reply #5 – March 08, 2005, 10:06:45 AM

Bah, I really hope it's not a vaccum leak, that'll take me forever to find. Granted it would be easier if it were warm out. Got any ideas on whether or not this would cause my gas milelage to go to ? I know that the cold and the type of gas most stations have help in that respect. But i'm curious to know if this stuff being outta whack would contribute to make it worse

. Oh, any ideas where to start looking for those vaccum leaks?

Re: Quick IAC question... I think.

Reply #6 – March 08, 2005, 06:57:28 PM

K, perhaps this may help for info on the prob. My idle more or less fixes itself after it's warmed up/ ran for a while. This is why I started leaning toward the IAC over the TPS or vaccum leak (which I didn't think of).

Re: Quick IAC question... I think.

Reply #7 – March 09, 2005, 11:27:27 PM

vac leaks are not hard to find,,you just gotta treat each color plastic tube as its own path.

these are the colors you have
black
green
red
tan
pink

take em one at a time, maybe one color a day.
plug off the far end and suck on the other.,, be a man :flip:
if you run into a "TEE" then troubleshoot each branch

I just sorted through the entire vac system on a full size bronco which the hood is 4 1/2 feet from the ground, now thats a beeyoch!!

If you undo the IAC, your just inserting a code to the eec. like said,, tinker with the tps
but
run codes afterwards and clear them out. run it for a while and see what codes are present then.

personally, it seems the idle control motor is doing its job,,,,, Its searching for something and it cant find it so it gives up and the eec defaults to a nominal setting after warm up and relearning the idle needs of your current engine situation.

your disadvantage from me is that you cant see the motor assembly plunger moving. Mine is completely exposed so i can can see it work.

another symptom on a non functioning idle control motor would be this. when you let off the gas,, you will feel an instant hard clunk in the rear of the car. The IAC or Idle control motor smooths out this for you. When you step on the gas, the plunger extends. When you let off the gas the plunger is waiting there for the trottle linkage lever to hit it. At that point, the iac retracts but acts as a shock absorber decreasing rpms. So it has two jobs,, to up the r's for warm up and as a gas pedal to rear differential buffer.

the boss of the iac would be the the eec and the tps.

Re: Quick IAC question... I think.

Reply #8 – March 10, 2005, 03:52:26 AM

Quote from: nirvanagod

K, perhaps this may help for info on the prob. My idle more or less fixes itself after it's warmed up/ ran for a while. This is why I started leaning toward the IAC over the TPS or vaccum leak (which I didn't think of).

Don't go chasin' a vac leak untill you've checked the other things I mentioned.... usually its the TPS...

Re: Quick IAC question... I think.

Reply #9 – March 15, 2005, 02:25:41 PM

Well I had the codes pulled today, and the only thing that came out was one for the thermactor air something or another not warming up or working (don't remember name or number

). But I was told that this could be in relation to have bad O2 sensors or the smog pump being froze up. Well, it was obvious that the smog pump was running, so i'd assume it's either the O2 sensors or, as was suggested, a valve of some sort was bad somewhere in the line

. Now i'm not 100% positive, but i'm pretty sure bad O2 sensors can cause bad gas mileage, but can they also cause the idle problem? I'm doubting it, but insight would be appreciated. Oh, are there any suggestions on the best type (brand) of O2 to get if the need presents itself?

Re: Quick IAC question... I think.

Reply #10 – March 15, 2005, 10:21:41 PM

Looked at the codes list, not sure, but it either came up with either code 44 (Air management system inoperative) or codes 81, 82 (Thermactor air bypass (TAB) circuit fault, Thermactor air diverter (TAD) circuit fault). I'm thinking it was more like code 44.

Re: Quick IAC question... I think.

Reply #11 – March 16, 2005, 08:19:41 AM

Usually when the diverter valve fails, if you stab the throttle at highway speeds and then let off it will let you know by burping air back into the system. Sounds like a backfire.....Mine went on the old 3.8 I had right befor I put the exhaust on. I used to scare the hell out of people in the car when doing this at night. It would sometimes ignite :flame:

Re: Quick IAC question... I think.

Reply #12 – March 16, 2005, 09:42:25 AM

Well i've had it at highway speeds, and have had to get off the pedal and get on it quick right away, but I can't say that it's ever backfired.
I'm thinking i'm just gonna buy oxygen sensors first, since it would be easier to take care of and knock out a possibilty if I still have problems.

Re: Quick IAC question... I think.

Reply #13 – March 16, 2005, 10:10:05 AM

Quote from: nirvanagod

Looked at the codes list, not sure, but it either came up with either code 44 (Air management system inoperative) or codes 81, 82 (Thermactor air bypass (TAB) circuit fault, Thermactor air diverter (TAD) circuit fault). I'm thinking it was more like code 44.

You can get a code 44 without having your AIR pump frozen up. I got a 44 code on my Cougar a while back, went through all the troubleshooting, and everything checked out ok. I replaced the pump ($35 + $10 core) and the code went away. The smog pump simply wasn't putting out enough air to pass the KEOR tests.

Re: Quick IAC question... I think.

Reply #14 – April 08, 2005, 12:22:03 AM

Figured i'd post an update on the situation. I just had the O2 sensors replaced, and man what a improvment! I've gotten the majority of my gas milage back (read 20+ city, not 10-15), and my idle has improved somewhat. Now on the subject of the idle. It's not perfect, but for now it doesn't seem to be hurting anything. So I think i'm going to let it ride as is untill I get the engine to stop bleeding oil like a stuck pig from the lower mainfold. What i'll most likely do is pick up some new vaccum tubing like Bird351 posted about in a couple of threads, and have that put on to replace the old stuff. But in the meantime, things are good and getting better!