IAC Air-BY-PASS Spacer Plate Idleing saga !!!

[Coleaclark]

Found the Real Part number $$ 71.00 part number F2Pz-9F939-A for anyone that could not find it

[smptx]

I just found one on E-Bay for 30.00 - going to install week after next . . .

[Coleaclark]

damn i just spend 65 on one at ford and have to wait to get it let me know how it turns out

[Seattle FSB]

Mmmm... Where have I seen this before? Maybe... How to Test and Clean your IAC


K-MansParts $49.95

Steeda Canada $54.99 (Canada)

CJPonyParts $67.99

FoxBodyWorld.com $67.99

Steeda US $69.95

Dallas Mustang $70.99

Idle Air Adjust Spacer

Allow me to elaborate on the Idle Air Spacer for a moment. Coking on Ford EFI Throttle Blades has been a problem for many years. If the PCV or vent filter clogs, oil tends to back up and accumulate in the Throttle Bore and plate. This is also caused by blow-by from worn piston rings in older engines. The oil becomes a sludgy residue which eventually hardens reducing the expected amount of air that can pass by the closed Throttle Plate. As less air passes by the closed Throttle Plate, the EEC commands the IAC to increase air flow around the Throttle Plate to maintain a good idle. Eventually, the IAC will approach edge of it's operating range. This is the point where the symptoms of poor idle are experienced and Throttle Body/IAC cleaning are indicated.

To alleviate this problem, Ford developed the Idle Air By-pass Service Kit (F2PZ-9F939-A) for EFI Broncos prior to MY1991. The kit includes an Idle Air Adjust Spacer that corrects sludge contamination concerns on the Throttle Blades to the point that Ford no longer covered Throttle Body Cleaning under the 5/50 Emissions Warranty. A secondary benefit is the ability to fine tune closed throttle plate idle air flow without altering the TPS, which has been very popular with Mustang performance builders having idle problems. The Idle Air Bypass Kit was installed by Ford Dealerships under warranty per TSB 91-25-07 and is still available from Ford as well as aftermarket versions from Tomco and eBay.

Beginning in 1991, Ford began using a Sludge Tolerant Throttle Body design which includes a special slick Teflon coating inside the throttle bore. This coating minimizes deposit formation and does not require cleaning or the service kit. The issue is harsh cleaning can remove the sensitive Teflon coating eliminating the protective qualities. These Throttle Bodies can be identified by a black/yellow sticker on the Throttle Body warning against cleaning or adjusting. Please note that this Sludge Tolerant Design does not include the IAC which may still require servicing or replacement.

[Coleaclark]

sweet cant wait for mine...

[miesk5]

yo, For DIY and to save $
"...I have spent some time this week trying to set up an air bypass around the IAC valve by cutting away some of the gasket between the IAC in and out air holes, rather than pay big bucks for Fords spacer kit. I cut away the center of the original IAC gasket from the outside of each hole to the outside of the other hole, giving about 1/2" gap for the air to pass through. I noticed an immediate improvement in the engines starting behavior, but it would still die occasionally. For most of my trucks life it has been dying when it was started hot. It would rev up and then drop the idle so low it would die unless I would catch the idle with the accelerator. It would never die when cold as the IAC would keep the idle speed up, and it never died at stop lights. Now it's worst situation seems to be when it has been shut down for a half hour or so, and restarted. I wonder if the heat soak is fooling the ETC into thinking the engine is warmer than it really is. I decided that more improvement could be had if I had a thicker gasket, because the original IAC gasket was very thin (0.018"). I had some 0.030" gasket material so I made my own with the same 1/2" cut out. This gave enough bypass to noticeably raise the idle speed and almost eliminate the dying. After maybe 50 starts in the last few days, it only died twice. After so many years of catching it with the accelerator it is darned hard to leave my foot off it. It is clear to me that by trial and error one can tune the air bypass without the need for the expensive Ford kit. I may combine the two gaskets for more bypass, but the idle is about as fast as I would want now, especially for driving in snow..."; Source: by Nelbur at Ford Bronco Zone Forums


miesk5 Note, Tomco makes an idle plate P/N 8491 = to Ford, P/N F2PZ9F939A; Like Ford’s service kit, Tomco’s spacer plate (arrow) is installed between the air bypass valve and its mounting boss using two gaskets. The two holes in the plate are for bleeder screws, which provide a minimum air rate adjustment independent of the throttle opening.

[Alvin in AZ]

Originally Posted by miesk5

yo, For DIY and to save $...

...had some 0.030" gasket material so I made my own with the same 1/2"
cut out. This gave enough bypass to noticeably raise the idle speed
-by Nelbur at Ford Bronco Zone Forums

The two holes in the plate are for bleeder screws, which provide a minimum
air rate adjustment independent of the throttle opening.

Cool post thanks, Miesk. :)

I was wondering how the plate worked and now understand what all them
holes and fittings are for. For the rest of us, that Ford decided we didn't need
the plate, making changes in the throttle plates' bypass holes is effectively
the same thing? Maybe, just not as "clean", I guess? <shrug>

What do you think?

The holes in the throttle plates can be sealed and new holes drilled, BTDT.

Alvin in AZ

[Mikey350]

Do all throttle plates have holes in them? My '94 does, and I wonder if Ford knew that the IAC wouldn't be able to handle all idle conditions, so Ford gave the throttle plates holes to help out.

[Alvin in AZ]

Originally Posted by Mikey350

Do all throttle plates have holes in them? My '94 does, and I wonder if Ford
knew that the IAC wouldn't be able to handle all idle conditions, so Ford gave
the throttle plates holes to help out.

Yeah, -that's- what I'm thinking too, because not all of 'em have holes and
I believe it's the older ones that don't. :)

The '90 F250 5.8 parts truck had holes in the throttle plates but they were
smaller than the holes in the '91 Bronco 5.8 and '91 F150 5.8.

I reduced the size of the holes in the Bronco and that allowed me to open
the plates a little wider and also made the "IAC unplugged RPM test" come
out right. :) The TB was getting "mechanically sticky", so needed opening
anyway IMO.

--------------------------

That reminds me.
For the guys that say -never-adjust-the-TB-...
Please read this sticker a little closer? ;)

Alvin in AZ

[Seattle FSB]

Alvin,

There is a difference between Base Idle and Curb Idle.

Base Idle
The idle speed determined by the throttle lever setting on the carburetor or throttle body while the idle speed control (ISC) motor, or any other computer-controlled idle speed control device, is fully retracted and disconnected.

Curb Idle
Normal idle rpm. Computer controlled on many modern vehicles.

Ford manually sets the Base Idle at the factory and the Curb Idle is set in the EEC programming. Curb Idle is not adjustable in EFI as it is controlled by the Powertrain Control Module. One should not alter the Minimum Air Flow expected by the computer unless there are significant modifications or someone has mis-adjusted the Throttle Plate Set Screw - and then only after disconnecting the IAC, adjusting to below Curb Idle, reconnecting the IAC, confirming proper TPS voltage and finally deleting the Keep Alive Memory.



In other words, the EEC will command a certain airflow for a specific rpm that it is trying to achieve. It then monitors the rpm to see if it's correct. If not, the EEC will adjust airflow up or down to hone in on the target idle rpm. If the IAC Airflow Function and Throttle Body Airflow Scalar values are not what the engine requires, the EEC can start hunting the idle up and down in an attempt to get the idle speed to the target value.

This is not to rule out the many other possible causes of a poor idle, such as:

- Vacuum Leaks
- Ignition Components
- Engine Timing
- Fuel System
- CANP
- EGR System
- Thermactor System

This brings us to "holes in the throttle plates". Fords original use of the Throttle Air Bypass Spacer Plate was due to warranty concerns of carbon build-up reducing Minimum Air Flow. They later redesigned the Throttle Body Butterfly Plate to include air bypass holes in order to accomplish the same task. The closed Throttle Plate position is communicated to the EEC via the TPS and the EEC expects a specific Minimum Air Flow. With that being said, significant aftermarket engine modifications, such as a lumpy cam, may require additional air flow to maintain a good idle. This is where you see some performance engine builders drilling out their throttle plates. Regardless, those who add or reduce expected Minimum Air Flow without addressing it in the EEC Programming are simply asking for idle problems.

--------------------------------------------

BTW Alvin, if you do go to the Ford Powertrain Control/Emissions Diagnosis Service Manual as the sticker requests, it specifically states "The curb idle and fast idle RPM are controlled by the EEC-IV processor and the idle RPM control device and cannot be adjusted". Ford cautions to only enter the Idle Setting Procedure after you have eliminated the possible idle problem causes listed below. In other words, an OEM idle requiring adjustment will always be due to one of these causes unless you have modified your engine or mis-adjusted your Idle Set Screw:

- Contamination within the throttle bore
- Contamination within the idle speed control device
- Contaminated or defected EGO/HEGO sensor
- Throttle sticking or binding
- Engine not reaching operating temperature
- Ingnition timing out of specification
- Vacuum air leaks (air intake manifold, vacuum hoses, vacuum reservoirs, power brake booster where applicable, etc.)


On a final note, turning the Throttle Set Screw in a "counter-clockwise" direction closes the throttle plate and each small estimated adjustment must be done with the engine off in order to reset the zero "Ratch" setting of the TPS. Ratch is the output of a ratchet algorithm which continuously seeks the minimum throttle angle corresponding to a CLOSED THROTTLE position.

[johnson33]

I have one on my car, they were used to fix idle problems do to the crappy iac valves. It doesnt matter how its put on it just lets air bypass the throttle body manually instead of the iac controlling it. I dont even have an iac on my car anymore i just use that spacer.

[tooquik89]

That part is GREAT. I have had one on each of the 5 5.0L mustangs I have had as well as 2 different explorers, and 5.0 F150 and now my 5.8 Bronco. These are great. When the IAC Motor goes, this is the way to go!

Online is always half the dealership price on these things.