Decelerating in my Mustang GT
11-22-2006, 04:41 AM
#1
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Decelerating in my Mustang GT
I understand that decelerating causes the most pollution from an engine. So modern engines have devices on them that keep them from decelerating rapidly. [:'(] Is there a way get around that? Would the"chip" help with that? I am old school using carburetors, points in the distributer and so on. I have a lot to learn. fd
11-22-2006, 11:18 AM
#2
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RE: Decelerating in my Mustang GT
The device is the engine control computer...and it allows excess oxygen to be scavenged from the cats on decel to prevent excess HC from gettting exhausted (I think). Yes it can be tuned out but I am not sure if that gives you a problem with your state emissions.
a little cleaner exhaust is not such a bad thing; I personally don't have a problem with the way it comes from the factory, but that is just me. You can still get a performance tune, I think, without making the exhaust dirtier....
a little cleaner exhaust is not such a bad thing; I personally don't have a problem with the way it comes from the factory, but that is just me. You can still get a performance tune, I think, without making the exhaust dirtier....
11-22-2006, 11:25 PM
#3
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RE: Decelerating in my Mustang GT
Thanks for this post, FordDude! I was wondering when this topic was going to pop up 
The problem I have with this "feature" is that engine braking is virtually useless until the computer decides it wants to fully close the throttle (usually like 5 seconds after you've taking your foot off the gas). If I wanted the "coasting" behavior of the automatic, I would have gotten an automatic...
This is the first time I've heard that you can actually tune this out of the car. Can we further confirmation on that? I agree that cleaner exhaust is better, but it would be nice to know what options there are for this. This feature is on my list entitled, "Annoying things about my car that are the result of micro-management by the computer, emissions-related or otherwise".
The problem I have with this "feature" is that engine braking is virtually useless until the computer decides it wants to fully close the throttle (usually like 5 seconds after you've taking your foot off the gas). If I wanted the "coasting" behavior of the automatic, I would have gotten an automatic...
This is the first time I've heard that you can actually tune this out of the car. Can we further confirmation on that? I agree that cleaner exhaust is better, but it would be nice to know what options there are for this. This feature is on my list entitled, "Annoying things about my car that are the result of micro-management by the computer, emissions-related or otherwise".
11-22-2006, 11:49 PM
#4
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RE: Decelerating in my Mustang GT
This is a very anoying trait. I've only got 2K miles on her so I've been trying to figure out if this is a problem or part of the comp throttle. I'm used to old direct linkage. When you remove your foot from the throttle it goes to idle. My 07 thinks about it for a few seconds then goes to idle. It doesn't seem to lower at all between gears(manual). I'd love to hear about a fix for it.
11-23-2006, 03:03 AM
#5
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RE: Decelerating in my Mustang GT
Cool Post, I despise this delayed deceleration trait on my 2007! I used to work for Nissan several years ago. They had a device on their earlier engines that was a mechanical decel device called a BCDD valve. (boost controlled deceleration device) It could be adjusted manually to stop it's operation. basically it was a variable vacuum leak that sensed manifold vacuum on decel and opened an orifice for a set period of time to control decel. With that said, I had hoped maybe that the ford system would be similar but it looks like it is not. If the computer controls it, then the programming should be able to be changed. All we have to do is find a guru who could figure it out. That might be the hardest part. I would love my engine to rev and decel immediately. It really sounds cool and makes downshifting a usable option.
11-23-2006, 02:44 PM
#6
Join Date: Nov 2006
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Posts: 35
RE: Decelerating in my Mustang GT
Do a search for IAC restrictor. It sounds like this gets rid of the "hanging throttle" problem which is what you guys are describing. I get my car in another month, so I haven't tried it myself yet. However, we drove an 05 for a while (was a demo from the dealership) and that was very annoying that the rev and in between shifts would hang. That's definitely gonna be one of the first mods on my ride.
11-23-2006, 02:47 PM
#7
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Join Date: May 2006
Location: Austin , TEXAS
Posts: 138
RE: Decelerating in my Mustang GT
I happened to get a Steeda CAI from someone in here , used , for less than 1/3 off , but not quite half price. It needed to have a tune to use it , and after reading this NG for about 6 months I decided to get the SCT X-CAL2 from brenspeed. Brent gives you 3 tunes for your car only <you have to tell him your Comp code> and I loaded the 87 octaine tune with the Steeda. Took care of the throttle lag right 0ff. Runs like a scalded dog!
11-24-2006, 04:51 AM
#8
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RE: Decelerating in my Mustang GT
I did a search of IAC restrictor and did not come up with anything. Then I Googled it. The info I found was a little old, that is the fix was for '03 Mustangs. But my question is will this work for our 05-07 Mustangs? Here is a pic of a IAC from a '98 Crown Vic. 
Here is a post about how to fix it. http://www.mach1registry.org/forums/...threadid=18330 If you do not want to click on the link here is a cut and paste.
I hope that is fix is as simple as this. I will have to check it out in the morning in the daylight. fd
Here is a post about how to fix it. http://www.mach1registry.org/forums/...threadid=18330 If you do not want to click on the link here is a cut and paste.
Hanging/Slow dropping RPM FIX inside.
Difficulty (1-10): 3
Time Required: 1 hour
Equipment: Socket set, .5square feet of 1/32" aluminum sheetmetal, tin snips
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 recieving 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 carburated 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 airholes, 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 "restricter 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.
Difficulty (1-10): 3
Time Required: 1 hour
Equipment: Socket set, .5square feet of 1/32" aluminum sheetmetal, tin snips
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 recieving 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 carburated 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 airholes, 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 "restricter 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.
11-24-2006, 11:02 PM
#9
4th Gear Member
Join Date: Nov 2006
Location: Now in Sunny SOCAL
Posts: 1,308
RE: Decelerating in my Mustang GT
Cool, sounds like the same type of system we used on the old nissans, an electric controlled vacuum leak. the engine computer also uses it to corect the idle speed when needed. IE when the A/C turns on. I'm gonna check it out. Thanks!!
11-25-2006, 12:53 AM
#10
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Join Date: Nov 2005
Location:
Posts: 176
RE: Decelerating in my Mustang GT
I think the mechanical device that everyone is referring to is the dashpot. It is a diaphragm that mechanically stops the throttle linkage from returning to the fully closed position for a second or two during decel. It is normally a separate unit from the Idle Air Control valve. With our Mustangs, since the throttle body is electronically controlled, there is no need for either of these devices. The electronic throttle gives much more precise control over these functions. Unfotunately, in their quest for reduced emissions, Ford decided to overlook the driver experience and program the dashpot emulation for max efficiency. Really sucks, as it is my biggest complaint about the Mustang. Luckily, a lot of it can be tuned out. You shouldn't have any issues during a smog check, as I don't know of any states that test emissions during deceleration.