93 Taurus Idles Too High

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Hi all, sure hope someone can point me in the right direction.
My Taurus GL, 3.0L auto runs great, when its happy, but lately what I am having is really high idle speeds after driving it for a while.
Start it up, drive a bit till its warm, and it idles as expected. Keep driving, and sooner or later, within ten minutes or so, when I get to a traffic light or whatever, the engine doesn't idle down to normal, but hangs way up there, like maybe closing in on 2000 rpm. (hard to guess) Makes life really interesting when I try to stop it :-)
I pull over, pop the hood, and try to force the throttle closed as a test, but it is closed all the way, no doubt about it.
Turn off the engine, and then start it back up, and its idling normally again. Sometimes it will repeat after a while, other times, it runs fine.
I have cleaned the throttle area to make sure no gunk is hanging things up, and even used a toothbrush on the inside of the throttle body around the blade. The cable is not binding.
I am not at all familiar with how the computer controls the engine speed beyond the throttle position sensor and am thinking the idle air control valve, but everything I have read, tells me the IAC will cause low idle speeds, not very high ones. I was told that if I unplug the IAC, and the engine stalls, its probably working okay, but perhaps that is a faulty statement?
I have a shop manual, but the idle control ckt is apparently addressed in the emissions control manual, which I cannot find for less than $275, so I am hoping someone might have an understanding of what controls what, and where I should be looking? Odd that turning the car off and then restarting "fixes" the problem, so I am thinking electrical, somewhere, but not sure where.
There is no check engine light, and no trouble codes when I have it checked.
Any advice would be appreciated,
John
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The IAC is just as capable of giving a high idle as it is a low idle.... When we start driving, the IAC moves to full open... this allows it to slowly close when the throttle is closed giving a "dashpot" effect..... The spring and the solenoid in this device are only so strong and it doesn't take much to make the spool hang in the bore....
Of course, we have checked to see if there are any DTCs in the PCMs memory, right?

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Acronyms kill me :-) As I mentioned, I hooked it up to the code reader, and it reported nothing. Is that what you mean by DTCs in the PCM? Is there more to check than using just the OBD1 reader?

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DTC = diagnostic trouble code. PCM = powertrain control module. Sorry for dumping acronyms on you.... that's just about all we speak in the shop any more... Some folks look at us like we're speaking in tongues.... 8^)
Shutting the car off will stop the airflow through the IAC... this could be enough to allow the spring to over come whatever may be hanging the valve open.... At idle, the PCM never runs the IAC duty cycle up to 100% so the IAC might not get to the spot on the pintle that is causing the grief. However, once you are underway, the IAC will be commanded to 100%ish duty cycle forcing it to full open....
My best suggestion - clean or replace the IAC and re-assess....
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I understand. I spent 25 years as an electronics engineer before I walked away. I miss the money, but not the acronyms :-)

That makes sense. I will do that this week. The Taurus shop manual says not to try to clean the IAC, only replace, but I have had so many people say they have cleaned it, that I figure its worth a try.
Thanks a lot for the explanation and the advice.
John
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But bafflegab is fun! Toss around those $25 words casually and confuzzle the hell out of everyone!

Of course the shop manual says to replace it, there's profit in just dropping a new one in, and none from cleaning the old one...
And a cleaning doesn't always cure the problem, so they don't want dealers cleaning them, it works for a few days, then it acts up again and the dealer ends up having to replace it for free when the customer complains.
If it's your money, you don't want to waste it - so try cleaning the IAC Valve first.
--<< Bruce >>--
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On Oct 21, 9:45 pm, Bruce L. Bergman

Yup, I agree. Its about Ford making money.
I took the valve off today and cleaned it. Didn't make any difference at all. I was hoping that it would make it a little better, or at least cause some kind of noteicealbe change, and then I would feel okay about dropping the $50 or $60 for a new one.
Everything I can find on the IAC seems to relate to low idle, or stumbling when cold. Haven't seen much of anything that points to the increased idle after driving for a time. Today I tested it after the cleanup, and it behaves the same, and always, when I pull over and its racing, I shut it off, start it up, and its all 'better' until I drive it again for five minutes or so.....
Unless I can figure out what else might be causing the problem that I could check, I guess I have to drop the coin and replace the IAC. Just sucks to buy parts willy-nilly hoping to find the real problem. <shrug>
Plus that awful feeling you get when you put in the new part, hoping against hope, and it still does the same thing :-)
I would guess that a vacuum leak would be more consistent, and would not 'reset' itself after the engine is turned off.
Thanks to all for the great input and comments. Very useful, and I appreciate it very much.
John
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Did you clean out the chamber that the IAC sets in, and the air passages in and out of the chamber? If the passages are plugged the valve can be working just fine but not do anything...
--<< Bruce >>--
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Bruce L. Bergman wrote:

Throttle position sensor?
--
Mortimer Schnerd, RN
mschnerdatcarolina.rr.com
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John wrote:

Take off your IAC valve and clean it out with carb cleaner or such. Check all vacuum lines around the engine and replace any that look cracked.
Bob
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Thanks Bob. I guess I will give that a shot. Hopefully it will at least make a difference, then I won't mind if I have to replace it. So long as I am confident it is the problem, I don't mind putting out the cash. Its not a cheap part, considering what it does <g>
Much obliged,
John
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Split the two halves where the rubber hose connects to the intake and check to see if the passage that connects to the IAC isn't plugged with carbon. Running a wire or air through there won't do it. kk
John wrote:

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Well, I appreciate all the pointers and ideas and am back to see if anyone can think of any place else to look?
I have replaced the TPS and the IAC, and found no difference in the symptoms. The throttle cable is not hanging, and when the idle heads up the RPM scale, if I get out and press the throttle blade, it is most definitely closed, and does not effect the engine speed to press it 'closed'.
If I just slowly drive around the neighborhood, it doesn't show the problem, runs fine, and the idle behaves. Its when I go out and run the speeds up to 40-60 mph, that when I come to a stop, the revs have climbed and will not come back down. I can then just let off the brake, and eventually end up in second gear, going 25 mph, its idle is that high. :-)
What is perplexing is, if I drive on the highway, pull off and the idle is so high, all I have to do is turn off the key, and restart, and its back to normal. In fact, just clicking they key off and on, quick enough to re-catch the engine, does the same thing, and returns the idle to normal without having to even restart the engine.
I think that rules out any kind of vacuum leak, or mechanical throttle issue, and points to the computer/sensors/electrical system?
No codes in the computer, and no idea what could make it do that. There must be a problem with a speed sensor, or something like that, as I would think that if the car was idling that high and not moving, the computer would complain about it somehow, wouldn't it?
Where, or what, is the speed sensor for this model? I have no idea where to look, as I don't comprehend how the whole circuit works, so any ideas or suggestions will be given my full attention.
Thanks a lot for the help,
John
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John wrote:

I still think you have some kind of vacuum leak somewhere. I would be checking and choking off vacuum hoses off the plenum at idle when this is happening and see if anything changes.
Bob
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Hi Bob, thanks a lot for the ideas. I am happy to have you beat me over the head with the vacuum leak idea :-) and maybe you can add some experience or something to help me get past this. I have certainly looked for leaks, but perhaps you know what I mean when I say I am "stuck" on it being something electrical, since it doesn't happen until I drive it over about 40mph for a few minutes, at which time, the idle is up around maybe 2K, and I can "fix" it from the driver's seat, but just switching the key off and on really quick, so quick that the engine doesn't have have time to stall. Then the idle, is back to normal.
That simply doesn't sound like a vacuum leak, although I am not saying it to sound argumentative :-) I just don't grasp all the concepts of the system. I don't know where the speed sensor is, and I don't know what kind of voltage I should be seeing at such a sensor, or at the IAC.
I have checked again to insure that the new TPS is installed properly, with the tangs properly aligned.
When the engine is running fast, I pull off the IAC connector, and it stalls right out, which I guess its supposed to do.
If its a vacuum leak, wouldn't it be more consistent? It could be vacuum on a device that is failing?
I have put a very good vacuum gauge on the engine in the past, and so if there was a leak that raised the engine speed that high, do you reckon it would show on the gauge?
I just think that the computer should be making a note of the fact that the car is not moving, and the engine speed is way out of spec, but I guess that isn't something that it pays attention to?
Augh! I hate to give Ford a hundred bucks to read the codes, and hundreds more to play "maybe its this, or maybe its that"........
Much obliged and willing to try almost anything at this point.
Have a good week.
John
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"John" wrote

Then grab a 2" piece of wire, and read the codes (if any) yourself.
The 93 is still OBD-I, just like my 88 Bird and Mom's 91 Taurus wagon. Use the bottom method of:
http://www3.telus.net/neatcrap/eec4.gif
The connectors should be strapped to the A/C piping on the passenger side under the hood. There's probably a plastic cap over them.
Insert the wire, get in the car, turn the key to "ON", and watch the Check Engine light do its blinky-blink thing. You'll get 2 sets of codes, each set repeated twice, with a separator.
Example: ( *=blink, .=pause) *.*.*...*.*......*.*.*...*.*.............*.............*.*...*......*.*...*.............
First set (problems found now) = 32 32(repeated) Separator = single blink after about 4 seconds Second set = 21 21(repeated)
You may get lots of codes, or just one (11 or 111 = all OK). Your codes may have 2 digits or 3. You'll likely get "now" codes that can be ignored, like Coolant Temp if the engine isn't hot, BOO if you don't press the brake, etc.
Pulling the wire while the light is blinking will clear all codes. Turning the key off after all codes have been read will let you read them again just by turning the key back on.
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I didn't know that method of clearing the codes. Thanks. The reader that I use is pretty basic, does several tests, and can reset them, but as I mentioned in another post just now, it appears that only Ford can recover some codes. Not sure I call that gospel, but between the mechanic, and a neighbor's experience, it appears to be true.
OBD1 is not all that complex tho, so I am not sure exactly what the facts are.
Thank you. The sketch helps a lot, as I do that with my older chevy to read codes. Never did know which pin was which to do it with OBDI
John
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Hello, I've been following your thread, as I have a somewhat similar problem with my idle. I have a 95 5.8 liter Bronco. I've been trying to fix it since July. My rpm climb happens only at startup, and once it settles down, it drives and idles perfectly. And it doesn't do it all the time, in fact, it went away completely for a month! Now it's back, but it's much less severe than it used to be. No codes, I can live with it for now. I'm totally with you on the dumping hundreds of dollars to a mechanic that might end up doing nothing, or even making things worse. (And yes, I took it to a Ford dealer, but quickly realized he had no idea what was going on.)
Reading your posts, I think sometimes I'm reading my own writings. I just thought I'd say you're not alone, and good luck. I'll be interested in how your situation turns out.
Another John
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i would get a scan that shows all sensor values while running if you can ,and try to interpret if each value is correct.. i have had several cases there were no codes and running problems did exist ,sometimes in the computer. i dont like the idea about replaceing a computer , but some fords ive worked on had this problem and a new computer fixed it .yes i did the test on the sensor values,engine vacume check, vac line inspect, fuel pressure test ,voltage check on the system.and a good scan.even did the iac and tps replace as a last ditch effort, but new computer did the trick.
http://www.minibite.com/america/malone.htm
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On Oct 26, 10:06 pm, snipped-for-privacy@webtv.net wrote:

How did you accomplish the scan of the sensors with it all running? The OBD1 reader I have isn't that complex. I am not even sure where to find all the sensors, as the shop manual isn't really for troubleshooting. I guess I might find more useful info in a chilton or something, at least for this issue.
I am not thrilled at paying a dealer a million dollars to do such a test, although I think you did the right thing, and I may be there soon myself. I having always taken care of my own vehicles, I don't really know of any shops that I trust to not just replace everything :-) Being your own mechanic can have its drawbacks I guess <shrug>
How much was the replacement computer?
Thanks a lot.
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