Hey Guys,
Hope I posted this in th right area, if not I appologize. I have a 2000 GT 4.6 SOHC, 5-speed. I have a problem. Not sure if it is a big one or not... When I rev the motor or when I am driving and shift, it takes forever for the rev to come back down to idle. I cleaned the IAC and it made no difference. The air filter is clean, and there are no error codes. It just seems to me that the throttle response isn't as fast as it shoud be. Anyone else had this issue? Any suggestions?
Thanks for any help...

 

You try running an upper engine cleaner through the car yet?

 

Not sure what an upper engine cleaner is...

 

sounds just like a vaccum leak or something with your intake is leaking

 

I looked for vacuum lines off or cracked but found nothing. The car runs flawlessly and I have no complaints but I just like the rev to fall off quicker. This is my first Stang so this may be normal... I have been looking at exhaust vids and it seems to me that mine is a bit slower falling back down to idle position.

 

Yeah, I've noticed that on mine too. stock 4.6 2 valve head ain't no hot rod head. I would say that maybe a port job or some better performing heads would give it a quicker throttle response. But the performance is still better than most stock heads. at least they are aluminum heads, not cast iron

 

my 02 v6 auto takes forever to fall down to ide too! I could pop her in nuetral and rev it up, and wait forever for it to fall down to a nice idle...

 

Its a common problem.

 

is there any fix or mention of possible solutions?

 

This is a super simple modification that you can do to your 99-04 Mustang GT 4.6 2v. With this mod you will create a new IAC gasket to fix the annoying RPM "hang" that stock GTs have. Have you ever reved up your engine and had it take forever to get back down to idle? This is what this mod will address and fix.

PROS:
- RPMs will return back down to idle faster. Makes for cleaner sounding revs without the annoying "hang".
- Engine braking effect will be present. Meaning; when you let off the gas, the car will actually start to slow itself back down instead of coasting.
- Makes the exhaust have the "gargle and pop" sound like an old hot rod when its on the down scale of a rev.
CONS:
- A "hissing" sound may be heard from under your hood when your standing near it. Sounds like a large vaccum leak. I believe this occurs because of the large amount of air restricted to the IAC by this mod.
- The vehicle may not be able to pass certain local emmisions tests. The reason our cars hang the RPMs in the first place is because of some emmisions crap Ford did. (Just keep your old gasket if you have to smog)
- You may have to re-learn the car a bit as far as shifting (manual trans. cars). The RPMs will fall faster and require you to shift a little sooner then normal.
- If you drill the hole too small, the car will not idle correctly. (Just make the hole bigger!)

As you can see, the Pros far outway the Cons, so go get your materials and tools and get to work!
Tools:
- Gasket Material: You can get this at any parts store like NAPA, Auto Zone...etc... It comes in a sheet, just tell 'em you need about 12'' x 12'' of it. Or, you can even use tin or thin rubber, I used gasket material to insure no air leaks.
- Socket Wrench (A socket extension is recomended)
- 8mm socket
- Ball point pen
- Drill
- 3/16'' drill bit (or even a 3/16'' punch may work if no drill or bit is available)
- A cardboard box
- Common household scissors

-1. Remove the PCV hose so you can access the lower IAC bolt, and remove the (2) 8mm bolts holding the IAC to the upper plenum. Remove the gasket. IMPORTANT: Keep the gasket somewhere incase you ever want to reverse this mod and/or you have to get a smog check!

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-2. Place the stock IAC gasket on the sheet of gasket material, and use a ball point pen to trace the stock gasket onto the sheet of new gasket material. Make sure to trace out the bolt holes on the sides of the gasket as well. Mark an "X" in the center of one of the large holes.

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-3. Using common household scissors, carefully cut out the new gasket following the lines you traced.

-4. Set the new cut-out gasket on top of a cardboard box. This will make it easier to drill (or punch) your bolt holes and center hole through the gasket without it ripping in your hands. Drill out your bolt holes using a 3/16'' drill bit, you may need to make a circualr motion with the drill in which it will "round" out the holes a little bit more. Test the sise of the hole by trying to push one of your 8mm bolts through the hole. If it doesn't go through, round out the hole a little more until it goes through with a snug and tight fit.
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-5. Using the 3/16'' bit (or punch), drill a hole straight through the little "X" you made in the center of one of the large holes. The size of this hole will determine how hard your revs fall or if your car will stay running at all and is the whole purpose of the mod. I've heard of people using 5/32'' bits for the IAC hole, I tried a 5/32'' bit and my car would not hold an idle and would die as soon as I let my foot off the gas, so I stepped up to 3/16'' and all was well. If this happends for you with the 3/16'' bit, then keep stepping up the size until your car runs properly and holds a nice idle.

-6. Now put the IAC back on with the new gasket (make sure the hole you drilled is on the side of the large hole in the plenum). Re-connect the PCV hose. IMPORTANT: Do not over-tighten the 8mm bolts back into the plenum!

-7. Fire up the car and check the idle. Make sure it holds an idle around 750-950 RPM or so, basically checking if it is idleing ok. Wait for oil pressure to build...etc... and give it a nice rev. Check to see if the car revs up clean and falls back down to idle with no problems. I've heard a few people talk about how this may affect a cold start, but I did this mod out in 18' F weather and the car fired right up. It won't go into a high idle, but it will idle never the less. ENJOY!!!!

Thanks to www.mustangforums.com and the members of MF.com for the ideas and inspirations for this write-up.

P.S.: Disposable cameras FTL!!!


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< Message edited by CoolAid -- 1/28/2007 7:18:13 PM >

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2004 GT Premium 5-Speed
All Alone, South of Heaven......


http://www.mustangforums.com/m_2625353/tm.htm

 

will the same apply for my v6 auto?

 

i just made a iac restrictor plate with a 1/4 in hole in one side and a 3/16s hole in the other to see which one i liked the 1/4 inch hole worked well for me but if you dont want to get it done that way you can get a tune or a tuner and turn the dashpot value down and it will adjust the amount of gases that are recirculated back through the intake tract.

 

Mariotraci,

I just finished trying what you suggested and it worked like a charm... .35 cents and 10 minutes and it runs like a new car! I wish all mods could be this easy and inexpensive LOL. Thanks guys for all the replies!

 

Brings back memories of things I used to do to get a car to run right, before I had tuning software.

 

what exactly is this IAC vavle and where is it located on the plenium?

 

its located on the front of the upper plenum. and its the Idle Air Control it lets unburned fuel and vapors back into the intake tract after you let off the gas. so the butterfly of your throttle body is closed but the unburned fumes are still circulating through the engine, causing the hanging rpm. if you restrict the amount of unburned gases going in the rpms fall much faster

 

I believe you are thinking of an EGR valve (exhaust gas recirculate) which is good for emissions. The IAC control goes after the throttle body, but has a tube that connects to the intake line that comes after the MAF, because if you think about it, if the throttle body is closed, how would air get into the engine? Thus, the IAC was born.

And I don't think that our cars have an EGR, but I could be wrong...

 

they do have an egr valve