Fix your Slow dropping/hanging RPMs

Discussion in 'SN95 4.6L Mustang Tech' started by magnum347, May 1, 2005.


  1. 02GTRX

    02GTRX I told an admin to shut up...now I live with the S

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    This mod actually helped my motor. Before in the mornings when I would take off it would hesitate kinda like a misfire until it would warm up, and now it takes off nice and smoothe. The ride also isnt as jerky as it was before when I would shift, now everytime I shift its very smoothe like an automatic. Do it and dont look back
  2. billfisher

    billfisher Active Member

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    the problem is idle mixture.

    i had this problem until yesterday with the 5.4.

    i added a little fuel pressure and the idle mixture was richer to the point it idled down and smooth. to check it remove a small vacuum port and if the idle gets worse look to idle mixture as the problem. how you are going to fix it for 99+, maybe look to a vacuum source to eliminate. but idle mixture was my hanging idle fix.

    i suspect it is the problem with aftermarket elbows also.
  3. stangGT97

    stangGT97 New Member

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    got one from Ebay for $7 shipped, made out of Mr. Gasket gasket material. Works like a charm, I'm very pleased :nice:
  4. USMstang

    USMstang Member

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    Done! That took all of 30 mins start to finish. I used some aluminum flashing. My GT only utilizes one hole in there (on the IAC), the other is dead space. Nice roll-off in rpm's, just like the carburetor days.
  5. 98blackstallion

    98blackstallion Member

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    hey guys i tried contacting the guy that makes these and he says that he cant make anymore can someone give me a link to how i can make my own or where i can buy one of them. Thank you
  6. trailblazr81

    trailblazr81 Member

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  7. hotrodnut

    hotrodnut Member

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    Contact Stangnet Member 34ford, he makes them.
    http://forums.stangnet.com/showthread.php?t=470711&highlight=34ford
  8. 98blackstallion

    98blackstallion Member

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    Well i did the copper cap mod and drilled a 3/16" hole in it first and put it in. Well then it didnt want to idle or anything so I enlarged it some more and I had to keep doing this for another 4 sizes up and then it started to work better. Maybe its because my car needs a tune? I have a full bolt on (minus plenum and TB) and stage 1 VT cams and still have the stockish tune. SO that might be my problem i will try it again after my dyno run next month.
  9. wht03GT

    wht03GT New Member

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    Bringin it back....

    Does anyone have a hiss after installing this when pressing the gas, or at idle?
  10. hotrodnut

    hotrodnut Member

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    Nope . . . no noise, no stalling, works as intended.
  11. sgarlic

    sgarlic Founding Member

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    Another bump for an old thread for new guys..

    I just made one of these puppies up today, and installed it. Both were a breeze.

    I borrowed a piece of brass stock from work, and removed the IAC. One wire harness, one hose, 2 5/16" bolts.

    Removed the gasket and the IAC assembly. Laid the gasket down on to the brass stock, and traced the outside and the 2 big holes with a magic marker. Used a scribe to trace the bolt holes.

    Used tin snips to cut the shape. Used different sized drill bits until I find one that was the right size for the bolts to fit through. Used a dremel with a metal spiral shaped bit to cut out one of the middle holes. I kept matching it up with the IAC to make sure the hole I cut was bigger than the IAC hole.

    Last fabricating step was drilling a 9/32 hole in the center of the other marked hole, and using a wire brush attachment on my dremel to clean up all the burrs. I threw it all back on, from front of car to back is IAC->plate->gasket->TB. I think perhaps I'll pick up another IAC gasket and put it between the IAC and the plate just to be sure.

    Impressions:

    Fired it up to be sure it worked. Ran fine. Turned blower to max, then switched to MAX A/C. Slight dip in idle as usual, but no stalling. Turned blower off. Switched to defrost and used max blower. Same dip in idle, no stalling. Rev'd to around 3k and let off. WOW. What a difference. Idle drops faster, but not annoyingly fast. Took it for a quick drive down the street, and noticed idle drops a lot nicer between shifts (not surprised since that was the whole point.) That "popping" when you let off I would call "cackling" instead. I noticed the delay from when you let off the throttle to when engine braking occurs is much less.. used to take 3 or 4 full seconds before I got full engine braking.. now it's easily less than 1/2 second.

    I'm still not sure about using brass, but now that I know how to do it, I may find some aluminum and use that instead.

    Great mod, took less than 30 minutes from start to finish, and cost me nothing.

    Thank goodness for whoever thought of this.
  12. WillDuhhBeast

    WillDuhhBeast New Member

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    I recently took mine out because it started to bug me. The rpm's would drop too fast from time to time then it would make it harder to shift smoothly. The rpms would drop down to 1500 and i'd have to ease out the clutch really slowly to not bounce it a little. It started to get really annoying. Having the rpm's "hang" for just a second allows a much smoother transfer through the gears, I noticed.


    I never noticed any "improvment" by this mod, beside the deceleration was slightly improved at certain rpm ranges, and the noise of it when decelerating.
  13. rocketman461

    rocketman461 New Member

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    Noise

    I have a "back-pressure" noise when I decel, but I don't have any constant hissing noise.
  14. 01GTSTANGER

    01GTSTANGER Member

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    I totally agree....I took mine out for the reason that my RPMS would drop so fast that when i would release the clutch I would hear a pop or something like that coming from my tranny. Took it off and my shifts were alot smother and no more popping. Loved the snap crakel and pop but dont want to damage anything. Just in case.
  15. GettinThere

    GettinThere Member

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    :nice:That settles it, I'm making one too.:nice:

    Thanks for your in-depth account. :nice: :flag:
  16. magnum347

    magnum347 Member

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    Awesome... just returned from Iraq again and this thread is still alive. I quit making these for awhile because of the new job in Balad Iraq. I'll make a bunch when I get back "over there" and will sell them again. And I will sell them cheaper than anyone.... with free shipping.
    Oh yeah.... Finally got a Paxton Novi 2000 Mongoose kit in my Bullitt from MPH.
  17. Warrior 102

    Warrior 102 New Member

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    I machine one from solid aircraft aluminum,I install it, and the car defiantly running the way supposed to run,nice mod.....
    I have left over material and I machine one more piece......now I have one extra...... here is some pictures.....
  18. rs-turbo

    rs-turbo Founding Member

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    Just thought I'd throw my five cents in here. I read this thread and liked the idea. I was going to replace my IAC since I suspected it was causing a stall issue now and then and figured I'd add this plate while I'm at it. I made a simple plate from a sheet of aluminum I had left over from another plate I once made for a different car to block off the EGR. My hole was a little smaller, turns out I didn't have the right drill size out of all the bits I've got. Once installed I had a high idle. It would vary between 1200-1500, which helped the AC and electrical with my underdrive pullies, but still annoying running so high. Everything seemed tight so it didn't seem like a leak past the plate. From what I've read with a smaller hole than mentioned here, I should have more of a stalling problem than high idle. The car did feel a lot more responsive and I loved the tougher sound of the popping. I intended to open the hole up a bit, but ran it "as is" for about two weeks when my Service Engine light came on. This past weekend I pulled the plate and reset the light by disconnecting the battery and right now all seems normal. Back to the standard idle, but now that I drove for a while the other way, I really miss the popping and the responsiveness. I now notice the idle staying high too. I don't recall it hanging this long before. This could be because the old IAC wasn't working right anyway and/or I just never paid that much attention to it. I've thought about trying the Mr. Gasket one on eBay, but figured an actual metal plate might be a better and more durable solution. Are you guys still putting a gasket on both sides of this plate, or just IAC/plate/TB? For now I'll see if my Service light stays off, or if I have another issue going on, and then probably buy one of the plates sold here when they are available again.

    Here's an idea for those making this. How about a screw or something in the side of the plate that extends into the hole. Then while installed if our idle is too low or high, we can simply turn the screw to open or close the hole some until idle become normal.
  19. loosescrew79

    loosescrew79 New Member

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    I have been thinking about taking mine out or maybe makethe hole a little bit bigger
  20. gtstangau

    gtstangau Member

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    I had to make the hole bigger, because the rpm's were sticking at 1500. Seems to work fine with the bigger hole. I love the crackling sound when I shift now! :D

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