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Discussion Starter #1
As many cars of this era have is the idle for the safety of braking with the hydroboost system. My car, before it hits a dead stop or nearly zero sits at about 1100, which is really annoying to me since its a decently loud ride. If I got a tuner for the car, lets say a superchips tuner, and I am able to have it idle normally, 700-900, would my stopping power be any less? Honestly ive delt with cars that have powerless brakes and these mustangs have brakes that really can stop the car.. when I bought the car it had a tune on it, I believe mainly because I installed the a/c and it would almost die at stops. I reflashed it and got the amazing factory settings again.. so if I was able to remove that annoying idle would my brakes still be able to stop?
 

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The "hanging idle" as it is commonly referred to is a function of the IAC valve, and from what I've been able to figure out it does so because it is actually somehow beneficial to emissions output.

Google "Mustang IAC rev mod". There are a couple ways to go about this; one involves making a restrictor plate that goes between the IAC and the plenum, you will need to drill a small hole about 3/16" - 5/16" or so as to allow for some flow. The other way is a 50cent 1/2" copper tube cap from the hardware store, with the previously mentioned hole drilled, and insert the cap into the tube just before the IAC. You will need to experiment a little on the hole sizing, so start small and work your way up. Too small and the engine won't idle or may die when you engage the clutch while rolling, and too large will be ineffective.

There is also a sticky about this over at mustangforums.com in the 4.6 section ("How To's") in case Google ain't your thing.
 

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The hanging idle never really bothered me....mine hangs around 900 or so (even though i have seen it drop to the 750 idle rpm plenty of times while coasting to a stop).

I think the only way to stop that is what Socal mentioned...

Keep in mind, this will also affect how the motor drops RPMs between shifts....for a DD like mine, i like how it hangs a bit, allows me to shift more leisurely when im cruisin around...dont really notice the hanging rpms when im hot-roddin ;)
 

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Discussion Starter #4
No, the hanging idle I "fixed" with the copper cap, makes it crackle more on down shifts so it makes the exhaust sound "better" but the thing I do not want anymore is the high idle rolling to a stop. It idles at about 1100 before I stop then drops down to 700-900ish once i stop fully. Id rather have it, once I push the clutch in, drop to the 700-900 range eventually. I believe the hole in my cap is 5/16ths but not 100% sure. The iac is a new oe replacement through oreillys. And I am pretty sure there is no vac leak. Iac stays around 40% once it runs awhile. But thanks for the information, it does not bother me is only bothers me when people think I want to race.. thats what I dont like since it has bassani mufflers and a catless midpiple. The exhaust is loud any higher, at idle, than about 900. Plus when I start it it use to rev up to 2000 rpms and then slowly idle down. Its still on a stock tune since it had to be reflashed.. really upset about that.. but it is what it is. Thanks for the advice though
 

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My car used to do that and it turned out it was a vacuum leak. If I were you, I would take a few minutes and just look at the plastic vacuum lines on top of the engine. They can get super brittle over time and leak in the weirdest places. Give one a squeeze and see if it immediately shatters in your hand (as mine did). Took me 4 dollars in vacuum hose and 10 minutes to replace all the vacuum line on top of the engine and it worked wonders.
 

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Discussion Starter #6
None of my vacuum lines are the issue since they arent leaking. Now, if I lean my ear over my throttle body, on the back side, I hear a sucking sound. But there is no vacuum lines that run on the back side of the engine that I know of.
 

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None of my vacuum lines are the issue since they arent leaking. Now, if I lean my ear over my throttle body, on the back side, I hear a sucking sound. But there is no vacuum lines that run on the back side of the engine that I know of.
The back side of the throttle body is where the vacuum line goes that goes to the EVAP system.

How do you know vacuum lines aren't leaking? Short of running datastream and checking fuel trims it's pretty hard to tell, and the only evidence seems to be something that MAY be a symptom of a vacuum leak.

If you hear a sucking sound at the back of the intake (may just be intake noise, does it whistle, high pitched?) maybe the EVAP line fell off the back of the TB. There is a vacuum line connected to the back of the throttle body that runs into a solenoid (for the evap) then continues down into another larger solenoid before finally running into the passenger side fender into the evap canister, then it returns.
 

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Discussion Starter #8
Fuel trims are within spec between -5 and +5. It actually rarely ventures from -1 and +1 still running on the factory tune with out cats. I will check tomorrow and see if the evap line is not disconnected
 

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I do not think the rollling idle can be fixed without a custom tune...it's an emissions thing that Ford built in to the tuning....all of our cars do it...

My EVAP hose connecting to the back of my plenum was so dry-rotted and disgusting..completely shot...put a new one on (about 6 months ago) and guess what the idle still hangs when stopping in nuetral or the clutch pressed in becuase it's an ECM issue, and one that is normal...
 

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Is there a difference in the computer between your "new edge" and my 97 and 96? Because the only time my car(s) rpms have hung like that was when there were vacuum leak issues (possibly IAC issues as well).
 
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