Ever Since I worked on my car...

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  • Witsend
    Banned
    • Nov 2012
    • 2942

    Ever Since I worked on my car...

    Some times you fix one thing and create 2 more problems . Changed a radiator in my 95 Explorer, and while the air intake tube was off I cleaned the throttle body with some throttle body cleaner and paper towels and gave the IAC passage a short burst of cleaner. Started the engine and the IAC is making a loud hooting, moosing, foghorn kind of noise .I Removed the Iac valve and found no evidence of piece of paper towel stuck in it. It's a metal plunger style , not the ribbed nylon style, so I clean it further with throttle body cleaner ,workec it back and forth and reinstall the IAC valve but it still made the obnoxious FogHorn noise. I take the MT2500 and put it through a KOER test and it passes the KOER test making the obnoxious noise the whole time. I also have a battery light illuminated on dash , but charging voltage looks fine. Fuses check good. I drive it to Advance auto to get a Digital analyzer print out to get a warrantee print out for a diode issue but no issue with charging is detected. I hook up the Counselor 2 and see a missing diode hump , every 6th place. I decide I want to check the IAC valve pattern but the goofy foghorn noise completely goes away before I can view the pattern with it making the sound but it wasn't making the sound. The RPM reads double what it really is because of waste spark system. Reran the KOER test and it has a KOER 411 code related to idle speed control . I don't know if good IAC pattern should look different , or not
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  • greasybob
    Senior Member
    • May 2008
    • 1590

    #2
    It would be helpful if I could see the time and voltage divisions on your scope screen. It almost seems to me like the PCM has a hard time grounding the IAC valve. I just checked my 96 Escort IAC and wave form is almost perfect square. Are you sure that your scope is grounded properly . It looks like you're IAC is running about a 25 to 30% duty cycle.

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    • diesel71
      Senior Member
      • Feb 2008
      • 921

      #3
      I have only scoped a few iac valves and remember the wave forum being a square pattern like bob has mentioned. might have a week iac valve, the amplitude curving to the right before peaking could be the sign. Ill have to check the next gas engine I get and compare. witsend your counselor 2 looks like a awesome tool.

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      • Trindaddy
        Senior Member
        • Jan 2010
        • 339

        #4
        Hey Wits. Actually, the foghorn noise was a pretty common thing in early 2000s when I worked for Mazda (Ford). Its a physical, resonant frequency anomoly regarding the IAC and the duct-work from the air filter and typically only lasted for a range of time during warm up. Ford issued a redesigned IAC to correct but I'll bet you could improve with almost any change in minimun airflow or the air ducts. You'll find a tsb if you look. "Foghorn" was exactly the descripter if my memory serves me. By cleaning and changing minimun airflow and IAC position, you have stumbled on the "magic" number.

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        • Witsend
          Banned
          • Nov 2012
          • 2942

          #5
          Hey Wits. Actually, the foghorn noise was a pretty common thing in early 2000s when I worked for Mazda (Ford). Its a physical, resonant frequency anomoly regarding the IAC and the duct-work from the air filter and typically only lasted for a range of time during warm up. Ford issued a redesigned IAC to correct but I'll bet you could improve with almost any change in minimun airflow or the air ducts. You'll find a tsb if you look. "Foghorn" was exactly the descripter if my memory serves me. By cleaning and changing minimun airflow and IAC position, you have stumbled on the "magic" number.
          Reply With Quote
          Lol, that noise stopped and the battery warning light went out shortly after too. I think the IAC valve might actually be DOA, because it idles too slow after a cold start and idle seems too fast when warm. I do not believe these IAC valves just default to a closed position with no airflow past them when unplugged. I will have to make sure the throttle blade stop actually is against the hard stop screw before I buy a new IAC , but until it stalls at stops with AC on or turning, I could care less. When I worked for Ford Some of the IAC's were bad out of the box and I think the TSB I remember described noise as a "Hooting Moosing Sound"LOL.

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