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93 4.0L Explorer w rough idle - replaced IAC - no change

Discussion in 'Under the Hood' started by grade_t, December 1, 2008.

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    1. grade_t

      grade_t New Member

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      Hi,

      after doing a fair amount of research I was convinced to change out the IAC (Idle Air Control) valve on my 1993 Ford Explorer 2WD 4.0L.

      My vehicle showing ALL these symptoms but ONLY after about 10 seconds at idle WHEN auto transmission at Drive setting (normal drive):

      a. entire vehicle - rock slight back and forth at idle
      b. volt guage rock back and forth about 2 to 3 volts from "normal'
      c. drop in RPMs from about 800 to 500 - feels like the vehicle is about to stall...

      move the car to N (neutral) and the problem abates by about 20%
      move the car to Park and the problem abates to about 30%

      replacing the IAC (where the old one tested electrically ok) didnt fix anything, sad to say. Wasted $60.

      Check Engine Light is not on.

      Car runs very well EVERY time it is not idling for longer than about 3-10 seconds. Ie, as long as engine RPMs are above about 1000 rpm, this vehicle runs fine.

      Ive also read that my vehicle's issue could be related to the MAF. If so, is there any danger to checking whether or not it is the culprit by simply removing it ?

      Any suggestions ?
       
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    3. grade_t

      grade_t New Member

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      after a bit more research I found this:

      If you have had bogging or missing or idle spots, about every 25K miles plan on this quick cleaning job:
      When your engine is cool, remove the wiring clip from the side of the black plastic sensor part of the MAF aluminum body. To remove the MAF interior sensor wire, you will need a Security Star (Size T15 or T20) screwdriver or screwdriver bit for a power screwdriver. Remove the two security star-head screws and carefully remove the sensor. You will see the two sensor filaments…they look almost like the filaments on a light bulb. Carefully spray the filaments with an O2 safe carburetor cleaner, such as Gumout. Let it dry thoroughly. I help mine along with a careful blast or two of canned dry air. While it is drying carefully wipe the aluminum mount surface of the MAF body if there is any dust there, but be careful not to get dust in the mount hole. When the sensor is dry, replace the sensor back in the MAF body and secure with the security star-head screws. These don't need to be torqued down, just simply hand tight. Replace the wiring clip. Then start up your engine. You should have solved any bogging or missing problems. My flat idle spot is ancient history.


      Im gonna try it and post back. Wish me luck !
       
    4. skoal_mint

      skoal_mint Active Member

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      also, try disconnecting some sensors and see if that helps..

      like tbs, maf... only unplug one then try another one, might mork but make sure you scan your truck first.

      I bet you have a code store somewhere
       
    5. sqhurt

      sqhurt Active Member

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      This is just a shot in the dark but my 93 would start an idle rough then one day it just wouldn't start.. Took my control module(the part all the plug wires go to on the top back of the motor) be sure to mark your plug wires so you put em back in the right spot. take the module to auto zone or auto store that can test it. Or if you have a volt meter an a chiltons you should be able to check it your self.. I believe my primary's went bad on it.. But if all else falls its worth a shot.. Just unscrew 4 bolts that hold the module on the bracket unplug a few harness an your plug wires... shouldn't take more then 15 mins to do it.
       
    6. Anime

      Anime EF YEAH!! Elite Explorer

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      Cleaning the MAF is always a good idea, especially if it's never been done.

      I'd suggest checking on basic stuff like air filter, plugs, wires, etc.

      Does it stumble or hesitate on hard acceleration? It might also be the fuel pump, or even the FPR (Fuel Pressure Regulator).

      In general though, that IAC has a LOT to do with anything at idle speed. If you're sure the one you have is good, or the problems happen no matter what IAC is on there, it's (obviously) something else causing the problems. My guess is it's either fuel pump or ignition related if the voltage meter is showing a drop, which means something electrical is going on.
       
    7. grade_t

      grade_t New Member

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      replaced IAC and cleaned MAF still have issue

      thanks to all for your helpful replies.

      After

      a. replacing the IAC
      b. cleaning the MAF
      c. replacing air filter
      d. replacing plugs
      e. replacing plug wires

      vehicle def runs better - but my issue remains.

      In addition:

      - RPMs, after about 20 secs, can drop suddenly from 800 to 500-600 and whole vehicle pitches back and forth (subtlely)

      - issue abates to about 70% when you drop from D1 to N

      - issue abates to about 65% when you drop from D1 to Park

      - after driving for more than 20mins the vehicle will actually stall in slow traffic

      - vehicle never stumbles or runs rough if other than idling


      Im still hunting around for the root cause ....
       
    8. Anime

      Anime EF YEAH!! Elite Explorer

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      If it runs fine when driving hard, and just stumbles or stalls at idle, even with all the new parts, I guess it's getting air and fuel. Might still be worth looking at the fuel filter, cleaning the throttle body and lubing the throttle linkage, but my guess now is it's sensor related. No check engine light when it stumbles or stalls?

      Also, did you disconnect the battery when replacing the sensor and doing the plugs/wires/MAF? Disconnecting the battery, leaving it disconnected for a long while, then reconnecting it and staring the vehicle, letting it idle for 5 minutes to relearn the idle/run program, then taking a spin for 5-10 min can let it adjust to the changes and make a huge difference in idle and performance.
       
    9. grade_t

      grade_t New Member

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      Hi Anime4x4

      thanks for your posts, and your help !

      "No check engine light when it stumbles or stalls?"

      it never comes on. Strange to me since it runs so badly at idle.

      I would agree it seems like a sensor problem. The condition at idle never occurs "right away" but only after a few beats at idle. Its almost always "all of a sudden too", by that I mean, vehicle comes to idle and then within about 10 secs - but no more - seems to heave backwards and forwards. Putting the vehicle in park seems to help it get by while waiting in (god forbid) bumper to bumper traffic or any red traffic light.
       
    10. grade_t

      grade_t New Member

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      what is meant by "tbs"

      hey Skoal - thanks for your posting.

      What did you mean by "tbs". Is that a sensor or ???

      Thanks,

      grade_t
       
    11. Justin Klare

      Justin Klare Member

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      check your vaccum lines. i tried everything but replacing the computer and i ordered one last week and it will be here this week. however my truck was doing the same thing and it ended up being a small crack in a vaccum line that was causing all my drama. i fixed the line and now my truck idles perfect and doesn't act like it wants to stall.
       
    12. grade_t

      grade_t New Member

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      Justin - thanks for the tip. It wouldnt surprise me at all that vacuum lines would be the problem. I searched for the best way to test them but still not sure I get it. Its a bit like the opposite of checking an inner tube for a leak I suppose.

      What vacuum lines ?
      Where are they ?

      I wish this was simple, but my car continues to run very poory at any idle.
       
    13. MrShorty

      MrShorty Well-Known Member

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      One thought: Where the stumble waits several seconds before starting, I would check O2 sensors. 1st step in checking the O2 sensors would be to run the self-tests. It's easy enough, I'd pull codes even though the CEL hasn't come on -- that doesn't always mean there isn't information the computer can give.

      I might also check fuel pressure: For whatever reason, it might have adequate fuel pressure upon initial startup, but after a few seconds, fuel delivery isn't keeping up with demand, and the pressure would drop off. Again, it would only take a few minutes to hook up a pressure gauge and see.
       
    14. lil_trucker

      lil_trucker New Member

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      I was wondering if you found a solution to your problem grade_t. I have the same problem, but it only happens intermittantly, and will go away after I drive it about 100ft and give it some gas.

      I am about to start going through everyone's suggestions, and was curious if you found a smoking gun?

      Thanks
       
    15. CrownRoyalRacing

      CrownRoyalRacing Member

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      I'm having a similar problem with my 96 XLT but it only idles rough when it warms up. I've completely rebuit the EGR system (at the same time I was getting an EGR code), new plugs and wires, cleaned IAC and MAF, checked my vacuum (it was good), and checked compression. I replaced the R/H upstream o2 sensor and it definately idles much better, but still a little rougher than I'd like. I plan on changing the L/H upstream o2 sensor soon. I think it might solve my problem. The R/H one was destroyed!!
       
    16. grade_t

      grade_t New Member

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      no solution in sight

      to all who posted here - Ive found no solution and my poor Explorer runs like crap, worse than before. Since this is not my area of expertise, I was hoping an expert would chime in here.

      Occasionally the "check engine" light will come on but Im not sure if thats related.

      Is it worth $99 to pay for a "diagnostic" to tell me whats wrong ?

      I wish some expert would chime in here !
       
    17. jlsparky7

      jlsparky7 Well-Known Member

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      Any weird noises? ticks, clanks, whines?

      Check for an intake leak. (spray carb cleaner or starting fluid around the intake tube and manifold and listen for the engine to rev up.)

      Compression test all your cylinders.

      Run some seafoam through it (how to is in my signature) when you do the seafoam check for exhaust leaks.

      Could be a plugged up catalytic converter. How many miles are on it?

      Have you ever ran a fuel/carbon cleaner? Might be a clogged injector as well.
       
    18. MrShorty

      MrShorty Well-Known Member

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      I don't know if I'm an expert, but I will chime in.

      Based on what local shops charge for computer diagnostics, $99 seems high, unless you know for sure the shop you are going to has some real special diagnostic expertise. Most shops around here want about 1/2 that, but I don't know that most of them are any more skilled than I am. If you aren't skilled enough, and don't want to spend the time/hassle/frustration (and frustration can be worth a lot of $$ sometimes) of learning how to diagnose it yourself, it might be $50-$100 well spent to get a good diagnosis.

      1st step in the diagnosis will be to pull codes. If you want to try this yourself, I would start with the instructional threads in the EEC-IV forum and try pulling codes yourself.
       
    19. ThePhoenix

      ThePhoenix Guest

      fuel filter....try changng that. It worked for me
       
    20. Fordnation1992

      Fordnation1992 New Member

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      2005 Ford explorer xlt v6 4.0l sohc rough idle

      Hi I got a 2005 ford explorer xlt v6 4.0l SOHC 4x4 an it has a rough idle an no check engine light and when I go to turn the defrost on, on the front windshield an i set it on 1 for the speed of the fan an my truck rpm's go up to 1000rpm or little higher also as I turn my front windshield defrost on you can hear my truck rev up an also can hear something click on an when my truck is off the rpm's eflucuiate plzzz help
       
    21. Fordnation1992

      Fordnation1992 New Member

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      Also I have no check engine light on
       
    22. Dpcx

      Dpcx New Member

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      rought idle

      i had the same problem as you, all the same symptoms and i changed everything, 2 o2 sensors IAC sensor, throttle position sensor, MAF, plugs wires fuel regulator, i even bought a scanner for codes. it kept giving me code 136/176 heo2 sensor and 113 122 ,, IAC and throttle position

      said it was running lean and it acted like it pinging and knocking but the plugs wet fouled ,, digging around i found it, it was the "air charge temperature sensor" ,, there is no code for it. its on the intake manifold on the drivers side towards the back,,, use a 1" wrench,, i took it off a lil sensor inside a cage ,, looks like a match head, it was bent over,, i pushed it back with a nail,, hit it with a ton of carb cleaner ,, put it in,, drove,, it ran like crap,, i kept going and then boom,, cleared up ,, runs great
       

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