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.
Why does this happen?
First, understand the problem. The engine is receiving too much air through the IAC valve. From my knowledge Ford did this for emissions reasons.
The plate fix:
First locate your IAC valve. Look on the front of your upper plenum, you will see a silver cylinder shaped object with 2 bolts holding it to the plenum and a black hose leading to it
In this pic it is the silver piece on the front of my red plenum
Pull the hose off the front, remove the two bolts and remove the IAC.
You should see that the IAC 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)
Making the plate:
Trace out the shape of this gasket as well as the holes for mounting bolts, and the two air holes, onto either a piece of aluminum sheet or a sheet of make your own gasket (found at most parts stores)
Cut out the outline of this "restrictor plate" from the sheet.
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.
This is what your finished plate will look like
After your "restrictor plate" is cut out, you are ready to install
Installing the plate:
Replace the gasket against the intake plenum, the mount the plate. Make sure the smaller hole you drilled is on the side of the large hole in the plenum and make sure to replace the gasket against the intake. Now put the IAC in place and bolt everything down. Replace the lage hose in front.
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 you are done and ready to 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 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.
Enjoy your non-hanging RPMs!
Why does this happen?
First, understand the problem. The engine is receiving too much air through the IAC valve. From my knowledge Ford did this for emissions reasons.
The plate fix:
First locate your IAC valve. Look on the front of your upper plenum, you will see a silver cylinder shaped object with 2 bolts holding it to the plenum and a black hose leading to it
In this pic it is the silver piece on the front of my red plenum
Pull the hose off the front, remove the two bolts and remove the IAC.
You should see that the IAC 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)
Making the plate:
Trace out the shape of this gasket as well as the holes for mounting bolts, and the two air holes, onto either a piece of aluminum sheet or a sheet of make your own gasket (found at most parts stores)
Cut out the outline of this "restrictor plate" from the sheet.
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.
This is what your finished plate will look like
After your "restrictor plate" is cut out, you are ready to install
Installing the plate:
Replace the gasket against the intake plenum, the mount the plate. Make sure the smaller hole you drilled is on the side of the large hole in the plenum and make sure to replace the gasket against the intake. Now put the IAC in place and bolt everything down. Replace the lage hose in front.
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 you are done and ready to 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 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.
Enjoy your non-hanging RPMs!
