IAC restrictor plate installed!

Discussion in '1994 - 1995 Specific Tech' started by R.J., Dec 31, 2005.

  1. After my Cobra intake install I had a hanging idle, so I did some searches on it and read about the restrictor plate for the IAC. It seemed everybody that used it loved it, so I had a couple made. I installed it today and WOW what a difference. My major changes were in start up and shifting, not so much in neutral revving. The car starts and settles a lot faster. Between shifts is the best, it seems like the car starts to pull before you get back into the gas. Between this and a mechanically setting your idle our cars idle issues can be dealt with! I would recommend this plate to anybody. I work with two guys that have Mach 1’s they are also going to try it because Mach 1’s are know for a hanging idle.
  2. what is a IAC restrictor plate? Do you have any pics? i've installed a cobra intake and my idle is absolutely atrocious! Pics would be GREATLY appreciated.
  3. omg i read about this awhile ago

    is there anyway you could send me pics of it?

    if it looks good i will send you money to cover shipping, materials, labour, everything.

    plz email me back [email protected]
  4. OK here is a pic of the plate, a link to an ebay auction, (I am not selling them) which has pics of the install on a Mach 1 (same exact install on a SN95 except the IAC is in a differant spot). Also here are directions to making your own:


    This is for anyone that doesn't like when the RPM's that are slow to drop or even rise slightly when you push the clutch in to shift. Another symptom, is that when cruising in a higher gear and you let your foot off the gas, the car almost cruises on its own for a bit.

    First, understand the problem. The engine is receiving too much air through the IAC valve. From my knowledge Ford did this for emissions reasons.

    As a side effect of this fix, when you downshift, the car burbles a lot more, sounds like a carberated engine. You get a little more engine braking effect.

    The FIX:
    Most older mustangs have an external IAC valve. Meaning that it is easy to find, follow a small air hose (1/2" ID) to a silver cylinder thing on your intake (the IAC solenoid). Once you found it, the older fix was to buy a 1/2" copper pipe cap, drill out a small hole, insert this into the line the restrict air flow through the IAC, and your done.
    The Mach has a slightly different setup.
    We have an INTERNAL IAC air supply. Meaning that there is no hose leading to it.

    To find your IAC valve, first remove your entire shaker assembly from your car.

    Next, look between your intake and the firewall, there should be a silver cylinder shaped object with 2 bolts leading to your intake.

    Remove the two bolts and move this assembly.

    You should see the following, the IAC assembly has two "ports" with the solenoid controlling the air flow between these two ports, what we want to accomplish is to restrict the airflow leading through this.

    To do this, there should be a small gasket on your intake, or it could be stuck to the IAC valve.

    Remove this (carefully)

    Trace out the shape of this gasket as well as the holes for mounting bolts, and the two air holes, onto a piece of 1/32" aluminum or something similar.

    Cut out the outline of this "restrictor plate" from the aluminum.

    Cut out the holes for your bolts to go through.

    Cut out a single one of the Air holes.
    Now the tricky part. You have to decide how big to make the other hole because this determines the amount of air you are restricting.

    The smallest you should go would be around 5/32", the worst case if you go to small is your car will stall when fix is complete, if this happens just take the plate out, make the hole bigger, and check that.
    The hole I used is around 9/32" which is about the medium you would want to go.

    After your "restrictor plate" is cut out, mount it with the small hole on the passenger side of the IAC, and make sure to replace the gasket against the intake.
    Start your car, you should notice the RPMs drop when you start back to normal very quickly.
    If it idles smoothly, try putting turning on the AC, this will load the engine down.
    If your car stalls out, remove the plate, make the hole bigger, try again.
    If still idling smoothly, bolt your shaker back on, take it for a spin. You might need to adjust your driving/clutching style after being used to the crappy RPM hang, so don't be discouraged.
    Also, you might want to disconnect your battery during the procedure to make your computer relearn it tweaks after you finish.

    If, after you start the car you notice a "whistling" sound, then take a look at your plate, make sure the BIG hole is at least as big as the hole on the IAC valve. Also make sure edges of holes are rounded (sharp edges are bad), and the holes are round. This happened on mine, and I fixed it.

    This subject has been talked about on Stangnet and a search will give you more opinions. I love it!!!!!!!!

    Attached Files:

  5. o are the plates for the sn95 5.0 and the mach 1 the exact same?
  6. Exactly the same. The only difference plate to plate is the size of the “small” hole, because all cars run different and some might need more or less air to idle. In the directions there is the smallest size that might work and the most common size, but any size that works is what you’re looking for. Mine was 3/16th, which is one above the smallest.
  7. you buy yours off ebay?
  8. No, I work at an Aircraft (Helicopter) Repair Facility and we have plenty of scrap sheetmetal and some of the best sheetmetal mechanics in the country. So I just bought a IAC gasket from a Ford dealership and used it as a template. The sheetmetal guys have lots of tricks and tools for centering holes and deburring, so the plates come out perfect. I will see how much metal we have and I'll see what I can do.
  9. I dont get it. Ford does not allow too much air to flow through the IAC with the throttle closed because that makes the car dump more fuel (to maintain stoichiometry). It wants as little air as possible to flow with the throttle closed (on the verge of stalling at hot idle, with no load). This should not be confused with the rolling idle, which is balky to prevent stalling (VSS and puter interaction).

    Some of the issue I have read and seen (IMHO) are from improper idle setting. I have seen some write ups that are backwards too. We know each car is different and each has individual issues. I would want to say that other ideas with setting the idle properly should be exhausted before adding another component to the mix (that was my main point R.J., as I know you played with the idle till the cows came home). I did not want to see everyone jump on the bandwagon when they had not even tried to dial in the base idle correctly.

    I am glad to hear that it worked out so well for ya. :nice:
  10. I totally agree and that is why I always push the point of mechanically setting your idle, to force the computer to learn a new baseline. On the other hand with or without a hanging idle, the throttle response between shifts is unbelievable now and my hanging idle has not fully gone away.
    So lets reestablish the points to be made here.
    If you have a hanging idle issue, YES you want to clean your MAF, clean this and clean that. Check for vacuum and exhaust leaks. There are a lot of good finds and cheap fixes out there for idle issues, do a search.
    Now that you realized you have to or want to adjust your idle, do it like this:


    Begin with a cold vehicle. The idea here is to get the car to a firm cold idle with enough air bleed capacity left in the idle circuit for IAC adjustment.

    The idle stop should be set first. Back out the idle stop screw, away from the bell crank arm, until about 1/2 turn past the point where it no longer makes contact (blade fully closed). Using a 0.010" feeler gauge, tighten until gauge just drags between screw and bell crank arm. Remove feeler gauge. Tighten screw exactly 1 1/2 turns. If the screw is very loose, put a drop of loc-tite or silicone on it, so it doesn't work out of adjustment.

    Now remove the connector to the Idle Air Controller (IAC) just on the other side of the throttle body. Start the car and allow vehicle to warm for 2 minutes. Give a small "blip" to let it settle. If it is having a hard time staying running you may have to get an assistant until you can get to the front of the car. Now open or close the air bleed screw (CCW opens) next to the IAC until the car idles at 575 to 600 rpm. For guys with aftermarket cams and an EEC tuner, you might want to idle a bit more briskly, say 650 to 675.

    Obviously, this rpm range is by what the car and driver wants...IE, no set idle speed, whatever works for YOU.

    Turn off the car. Now count the number of turns clockwise to close on the idle air bleed screw. If it falls between 1/2 and 2, it's okay, now reverse it out the same number of turns. Log the number somewhere in case you need it for the future. Reconnect the IAC. You are done.

    If the air bleed screw is above 2 turns, it's a good idea to tighten the idle stop screw another 1/2 turn, and then repeat the idle setting. If it is below 1/2 turn, then loosen the idle stop screw by 1/4 to 1/2 a turn, and repeat the idle setting. Be sure to put another drop of silicone RTV on the stop screw if it was disturbed. Reconnect the IAC. You are done.

    Now if this worked, your happy, I’m happy and now you can think about doing the restrictor plate for the between shifts response factor or leave it as.
    Now if it did not work, the plate might help and also give you better starts and better throttle response. If the plate does change your idle, just a little, maybe try mechanically setting it after the plate is installed!
    Again, my idle issue is not gone but this plate changed the performance of my car enough for me to think it was worth my time.
  11. i would be interested in one too
  12. that would be awesome man

    if you can do it, just lemme know how much
  13. I assume that does what this does http://www.steeda.com/store/-catalog/idlebypass.htm [​IMG] only the Steeda part is adjustable? So is the plate smaller than the gasket?
  14. One hole in the plate is the same size as the hole in the IAC and the other hole is any where from 5/32nd to 5/8. What ever works best. The 3/8 to 9/32 range seems to be the best.
    I don't konw if Steeda's plate does the same thing or if it works at all. For $32 they can keep it!!
  15. all i know is i hate the hanging idle:bang: :bang: and in between shift and will be trying this soon:hail2: or putting on a fox tb which i have heard does the same thing
  16. YEAHLOH95: Have you tried mechanically setting your idle with the steps I posted above?
  17. my idle is fine at 900 with my cam but it the "other " things i can't stand, not idleing down at a red light and in between shifts
  18. Troy
    Only cure for mine with that was the fox tb swap.

    The plate works great..my car idles rock solid at 800rpm
  19. I had 11 plates made today and I will GIVE one each to the first 11 people to send me there name and mailing address. I figure that is the only fair way to distribute them. All it is going to cost me is stamps! Big deal!

    The plates are drilled with a 3/16th "small hole", so if your car will not idle (with or without A/C on) then the hole will need to be drilled one size bigger and so on and so forth. Again 9/32 seems to work best, mine worked perfect at 3/16th. I will send a copy of the direction along with the plates. Ok send your info!
  20. sent you a PM :nice: