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Thread: 89 5.0L Mustang- Hunting/ Surging Idle Problem- Please HELP

  1. #1
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    89 5.0L Mustang- Hunting/ Surging Idle Problem- Please HELP

    Okay guys, so I'll cut right to the chase. Ever since I bought my 89 5.0L mustang 7 years ago, it has had an idle surging/hunting issue that is extremely annoying and worrisome to me, that I have not yet been able to find the problem to. Now before everyone yells out at the same time that its my Air Idle Control Motor, I have already put a lot of research into finding out what the problem is, and it appears from my voltage test that my AIC motor is working fine, however I am not sure how "disfunctional" such a simple device can be, or faulty if you will, versus completely not working. It seems to me an AIC either works, or it doesn't. Now here is a list of things I have tested so far, and replaced and still has not fixed the problem. But before I do i will use this youtube link that PERFECTLY describes my idle surging and hunting issue :

    http://www.youtube.com/watch?v=Hcbpos_fN3c

    The surging issue seen here for the first 30 seconds of the video is my problem (it has never been so bad that it has actually stalled on me). Now I have temporarily been able to fix the problem by having the idle set to a higher than normal rpm, which is about 900-1000 when cold, and about 1100 once it has heated up. Here is the list of things I have tested or replaced so far:

    -Replaced TPS, got rid of the hanging rpm upon deceleration, but did not fix the idle surging.

    -Checked AIC Motor for proper voltage, proved to be fine (have no yet removed it to check if it is extremely dirty or not but i have heard cleaning it never totally fixes any problem associated with an AIC)

    -Replaced Engine Coolant Temp Sensor, as well as Air Charge Temp sensor as i heard these can also cause erratic idle problems)

    -Had Joe Dasilva clean and reinstall the MAF sensor, was dirty but didn't help anything

    If anybody has any suggestions i would GREATLY appreciate your input. I don't like fixing problems by covering them up (boosting idle speed to fix surging).

    Also it appears I have a steady miss and i get HORRIBLE gas mileage in the city as well, but i have yet to see if that will have been fixed by replacing the two sensors)

    Thanks guys!

  2. #2
    Been around a LONG time Ponyryd's Avatar

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    7 years? have you ever had a mechanic look at it? it really sounds like you should fix the misfire/fuel mileage issue first, but the problem is likely a bad IAC. when you did the TPS did you set the voltage and check the sweep?

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    My mechanic is Joe Dasilva, and I couldn't believe he had no suggestions for me when trying to fix the surge problem. Now i did set the voltage and check the sweep on both the OEM unit, and the new unit, and I made sure the voltage was at the proper level when i positioned the new TPS on top. It was a bit high (1.1, and i couldn't get it any lower, so i had to adjust the idle speed knob down a bit to .99v, but then once I started it up again the speed was too low, so i had to adjust it back up again. It's a vicious circle for me with this problem unfortunately.

    Now my next thing to try is I am going to take it to a Ford dealer Monday and ask them if they have proper equipment there to scan this vintage of mustang to get proper fault codes, but people keep telling me there is limited codes you can retrieve for a mustang this old :(

  4. #4
    Been around a LONG time Ponyryd's Avatar

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    There is, but anyone can scan it, it likely won't help much unless something is actually broken/failing. If your t.p. was at 1.1 at it's lowest and the car wouldn't idle at .99 it likely needs an IAC or has a vacuum leak somewhere. What are your mods/work that's been done?

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    Sorry if i mislead you, it WOULD idle pretty decent at .99v, but it was around 700, and it was a bit rough, but that could in part be because its an old Ford V8, I'm not quite sure. The reason I bumped it up again was because after i let it warm up idling for about 10 minutes, it started to surge again quite bad and i was worried it was going to stall out, so i bumped it back up to 900 which helped, but it was still moving around a bit.

    If you mean mods to the engine itself, not much at all. Cold air intake was done a long time ago. I had the heads sent out to the states to get shaved and straightened because the cylinder head gaskets were leaking oil, so I got everything polished and bolted down and all that is fine now. I have headers, on-road h-pipe, and aftermarket exhaust, but thats unrelated to any of my issues. I have many mods done to other things such as suspension, chassis stiffening, and brakes, but again unrelated to my issue.

    I have replaced the plugs, but NOT the injectors. It has 8mm aftermarket spark plug wires, and an OEM distributor system.

    Anything that may have been messed around with before i took ownership of the car, i have no idea...There were an alarming number of private, and dealer owners before myself, but the car was mint when i bought it with the exception of the idle problem.

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    What is the most reliable test to justify whether my AIC is working properly, or if its "faulty"

  7. #7
    Been around a LONG time Ponyryd's Avatar

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    It's tough to test, you need an electronic tester to actuate it, but even that won't tell you if it's intermittantly hunting as you describe. 700rpm is about right, should be no higher than 800. Most likely causes are vacuum leak or bad IAC, it would be pretty easy to find someone here to lend you one to put on as a "test" part. I had a few in my tool box last time I checked but they've been there for years so they may be siezed up, plus I'm a bit far.

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    Well I appreciate your offer very much. I am almost POSITIVE it is not a vacuum leak, as you cannot hear any sucking or whistling sounds, and also a vacuum leak would not be reliant on temperature of the engine, or run time, and that's the situation right now for me. Do you mean somebody would lend me a spare IAC to test on mine, or the electronic tester to operate the IAC? The test i did before was just using a voltmeter. Perhaps that wasn't the proper test?

  9. #9
    Blowin ALOT of hot air ! b-blown's Avatar

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    way back when there was a factory recall for that very problem and it actually started with F-Series trucks and the fix migrated onto Mustangs basically its an extra air bleed to smooth out the problem ..i am not sure if Ford still stocks it (doubtful) but CJ Pony Parts still sells it
    http://www.cjponyparts.com/idle-air-...1993/p/HW2451/

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    So is this like a gasket that is different from the original? Is it NOT a problem with the AIC motors itself, but rather with one or more of these pieces? I apologize if i do not know the correct terminology to use but I am very grateful for your input if you could just clear up for me exactly what the issue is and what needs to be replaced.

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