Idle air bypass Ford: F2PZ-9F939-A - Ford Mustang Forum
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What do y’all think of these? Originally they were designed to stop “crud” from forming on the throttle body but people use them to try and solve surging idle and other idle related issues. It looks like it works for some but not others. Right now I have my TB blade opened enough to where it will stay idling with the fan running. It works but the idle will hang and then surge a few times before it settles down when coming to a stop. Prior to raising the idle it would die when the fan came on. I think it surges because I have the idle set too high and the ecu is trying to correct it, but I’m not 100% on that. With this device supposedly one can close the TB blade and “open the IAC” enough to where it’ll idle.
Anyone ever tried one? I know about the resrrditor plates that people make that reduce the amount of air coming in through the IAC, but an adjustable one seems like it’d be more user friendly if it works. Anyone with a lopey cam that has had idle problems ever tried the adjustable one and it worked? It’s kind of an expensive gamble at $60-$70.

https://www.cjponyparts.com/ford-idl...1993/p/HW2451/

https://www.google.com/amp/www.fulls...a.html%3famp=1

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Nothing really new, I made one up for the EGR valve on my F150 1990 SWB 5speed truck.... to address the part throttle hesitation...… very well known issue back then. Are you sure you don't have a tiny/partial vacume leak?


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Nothing really new, I made one up for the EGR valve on my F150 1990 SWB 5speed truck.... to address the part throttle hesitation...… very well known issue back then. Are you sure you don't have a tiny/partial vacume leak?
Not 100% sure, but I don’t believe so. Prior to raising the idle the motor would die when the IAC was disconnected. So I raised the idle to where it would stay running with it disconnected and I plugged it back in. So now the idle surges some when it’s trying to settle after the motor has been revved. It’ll also surge a little once at a complete stop. It’ll surge a few times and then even out and idle steady.
Also prior to raising the idle It would idle well for a good 30 minutes or more. But when the fan came on the idle would surge iratically and often times it would die. If you revved it up it would usually “straighten out” and idle for a bit longer, but sometimes you had to keep it revved up to keep it going. It did, and does run down the road well. It just wouldn’t idle after the motor was warm, and turning on the accrssories exacterbated the problem. Sounds like it could be a vacuum leak but I think it’s really an IAC issue. I think there’s probably a short in the wiring actually. But it’s staying running via opening up the TB. I might just have the idle set too high though. I believe if it’s set over 750 rpm that the ecu will try to take over to get it to where it wants it. I’m not sure where it is exactly because my tach reads high. That 750 (if that’s the right number) might not apply to me though because it might have been changed via tuning. I can’t remember where it used to idle exactly. I just need to play with it some more, and possibly take a gamble wasting money on one of those adjustable rigs.
Sounds kinda like a vac leak but it would idle forever until it started having problems and it wouldn’t run or start with the IAC unplugged and I believe it’s supposed to be able too. If it won’t rumor has it that the TB isn’t open enough and or not enough air is going through the IAC.
Did the plate work on your egr problem?
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Did the plate work on your egr problem?
Yes....truck ran smooth as silk! IIRR, the original ports were 1/2" diameter and the restrictor I built ended up with 3/8" diameter holes.


IMHO, time for a smoke test and if that doesn't show something then either the IAC or I have had TB's do the same thing.
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Did the plate work on your egr problem?
Yes....truck ran smooth as silk! IIRR, the original ports were 1/2" diameter and the restrictor I built ended up with 3/8" diameter holes.


IMHO, time for a smoke test and if that doesn't show something then either the IAC or I have had TB's do the same thing.
I couldn’t get the idle stop screw to turn on my old TB so I bought an aftermarket TB that I was able to adjust. When I put the new TB on it wouldn’t start with or without the IAC plugged in until I opened the throttle a little. When I say I raised the idle it was barely. The throttle blade is still closed it’s not “revved up.” It still idles what sounds like an idle speed. I don’t think the throttle is open enough to compensate for a vac leak if that was the original issue. My original thought when I discovered it wouldn’t idle w the IAC unplugged was that somehow the TB blade was closed more so than it used to be since the stop screw had never been turned. So I stuck a nickel and penny under the stop, the motor ran with the IAC unplugged and it didn’t stumble when the fan came on. So off to get a new TB I went and that brings us to today. Idle too high and the ecu is “fighting” the stop screw until it settles down. Or maybe the idle is high and also there’s too much air going through the IAC as well. I guess really I need to check out the wiring. But if I indeed to Gerry rig it with a new TB maybe a little more rigging with the IAC will get it good enough. It’s running at 90% ok now. Livable.
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What do y’all think of these? Originally they were designed to stop “crud” from forming on the throttle body but people use them to try and solve surging idle and other idle related issues. It looks like it works for some but not others. Right now I have my TB blade opened enough to where it will stay idling with the fan running. It works but the idle will hang and then surge a few times before it settles down when coming to a stop. Prior to raising the idle it would die when the fan came on. I think it surges because I have the idle set too high and the ecu is trying to correct it, but I’m not 100% on that. With this device supposedly one can close the TB blade and “open the IAC” enough to where it’ll idle.
Anyone ever tried one? I know about the resrrditor plates that people make that reduce the amount of air coming in through the IAC, but an adjustable one seems like it’d be more user friendly if it works. Anyone with a lopey cam that has had idle problems ever tried the adjustable one and it worked? It’s kind of an expensive gamble at $60-$70.

https://www.cjponyparts.com/ford-idl...1993/p/HW2451/

https://www.google.com/amp/www.fulls...a.html%3famp=1

https://www.google.com/search?q=Ford...&client=safari

If you crank the idle up to compensate for load (ac,fan,etc) & it puts the mechanical idle speed out of the range the ecu needs it to be in,in order to control idle via the iac valve,surging can definitely begin.Other than being used for a cold start,the next most important reason for an iac valve is load compensation.If you have to increase the idle by a couple hundred rpm to help with that load,thats definitely gonna work against the ecu for idle control.


(Idle Air Adjust Spacer)copy/pasted
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.

1991 Mustang lx
D.S.S. 342ci {10.5:1}
TFS 190cc + track heat
Lunati 61011 .549".565"
Pro-M 76mm maf
Jetronic 30lb inj
QA1 Coilovers
17" Weld ProStar XP's
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post #8 of 21 (permalink) Old 4 Weeks Ago Thread Starter
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Quote:
Originally Posted by wbrockstar View Post
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Originally Posted by 90lxwhite View Post
What do y’all think of these? Originally they were designed to stop “crud” from forming on the throttle body but people use them to try and solve surging idle and other idle related issues. It looks like it works for some but not others. Right now I have my TB blade opened enough to where it will stay idling with the fan running. It works but the idle will hang and then surge a few times before it settles down when coming to a stop. Prior to raising the idle it would die when the fan came on. I think it surges because I have the idle set too high and the ecu is trying to correct it, but I’m not 100% on that. With this device supposedly one can close the TB blade and “open the IAC” enough to where it’ll idle.
Anyone ever tried one? I know about the resrrditor plates that people make that reduce the amount of air coming in through the IAC, but an adjustable one seems like it’d be more user friendly if it works. Anyone with a lopey cam that has had idle problems ever tried the adjustable one and it worked? It’s kind of an expensive gamble at $60-$70.

https://www.cjponyparts.com/ford-idl...1993/p/HW2451/

https://www.google.com/amp/www.fulls...a.html%3famp=1

https://www.google.com/search?q=Ford...&client=safari

If you crank the idle up to compensate for load (ac,fan,etc) & it puts the mechanical idle speed out of the range the ecu needs it to be in,in order to control idle via the iac valve,surging can definitely begin.Other than being used for a cold start,the next most important reason for an iac valve is load compensation.If you have to increase the idle by a couple hundred rpm to help with that load,thats definitely gonna work against the ecu for idle control.


(Idle Air Adjust Spacer)copy/pasted
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.
Yeah the theory/hope with using one I think is that I’d be able to close the throttle more with that thing in there and it would still idle. You know, maybe I can lower the idle to where it wouldn’t surge but also stay running with the fan on.
I dunno. Maybe I’ll play with the idle this weekend and go from there. If the plate was say $30-$40 I’d be more willing to take a gamble on one. But at $60-$70 that’s kind of an expensive crap shoot.
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post #9 of 21 (permalink) Old 4 Weeks Ago
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I'd make a trip to pull-a-part if youve got one and look around the Ford isle before I'd spend that kinda money on one.Heck that part may be considered a pocket item,but I try not to walk out the door with anything until I have asked to make sure.Generally if the counter person doesn't even know what the part is called,they'll just wave you thru anyways since they dont know what price to charge anyway.The plate works for some and it doesn't work for others,so youre right in your thought process about being reluctant to spend that kinda cash.It worked for my lx when I had a Ecam,but there was likely something else wrong that the plate was just acting as a bandaid for.I'd go check all of the late 80's-90 Broncos and other 5.0/5.8 Fords near that year range and see if you can locate one.Its only $1 entrance fee with vip card or $2 otherwise,to get in pull-a-part to look around.If I knew where to look in my disorganized garage,I'd send you the one I bought years ago,but finding it would be the ???.I may have some time tomorrow to search for it though and if I locate it,I'll drop a note here or thru a pm.

1991 Mustang lx
D.S.S. 342ci {10.5:1}
TFS 190cc + track heat
Lunati 61011 .549".565"
Pro-M 76mm maf
Jetronic 30lb inj
QA1 Coilovers
17" Weld ProStar XP's
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Originally Posted by wbrockstar View Post
I'd make a trip to pull-a-part if youve got one and look around the Ford isle before I'd spend that kinda money on one.Heck that part may be considered a pocket item,but I try not to walk out the door with anything until I have asked to make sure.Generally if the counter person doesn't even know what the part is called,they'll just wave you thru anyways since they dont know what price to charge anyway.The plate works for some and it doesn't work for others,so youre right in your thought process about being reluctant to spend that kinda cash.It worked for my lx when I had a Ecam,but there was likely something else wrong that the plate was just acting as a bandaid for.I'd go check all of the late 80's-90 Broncos and other 5.0/5.8 Fords near that year range and see if you can locate one.Its only $1 entrance fee with vip card or $2 otherwise,to get in pull-a-part to look around.If I knew where to look in my disorganized garage,I'd send you the one I bought years ago,but finding it would be the ???.I may have some time tomorrow to search for it though and if I locate it,I'll drop a note here or thru a pm.
Thanks bother. This weekend if the weather holds out maybe I’ll get some time to play cars and that’s a good idea about browsing the pull-a-parts. $70 would be ok I guess if I knew it’d work. But if it didn’t that’d be fairly bunk.
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I'd make a trip to pull-a-part if youve got one and look around the Ford isle before I'd spend that kinda money on one.Heck that part may be considered a pocket item,but I try not to walk out the door with anything until I have asked to make sure.Generally if the counter person doesn't even know what the part is called,they'll just wave you thru anyways since they dont know what price to charge anyway.The plate works for some and it doesn't work for others,so youre right in your thought process about being reluctant to spend that kinda cash.It worked for my lx when I had a Ecam,but there was likely something else wrong that the plate was just acting as a bandaid for.I'd go check all of the late 80's-90 Broncos and other 5.0/5.8 Fords near that year range and see if you can locate one.Its only $1 entrance fee with vip card or $2 otherwise,to get in pull-a-part to look around.If I knew where to look in my disorganized garage,I'd send you the one I bought years ago,but finding it would be the ???.I may have some time tomorrow to search for it though and if I locate it,I'll drop a note here or thru a pm.
Also how about the “restrictor plates.” The ones with two smaller holes in them that block the air. Are those supposed to do the same thing as the “adjuster” except ones adjustable and the other isn’t? Or are they two different animals?
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I went ahead and ordered one from Late Model Restoration and it’s supposed to arrive Friday. If it doesn’t work I’ll see if I can send it back.
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Also how about the “restrictor plates.” The ones with two smaller holes in them that block the air. Are those supposed to do the same thing as the “adjuster” except ones adjustable and the other isn’t? Or are they two different animals?

I dont have any experience with the use of a restrictor plate,but going by the image & reading its description,its main purpose appears to be for the prevention/reduction of a hanging idle that occurs between shifts & when in neutral,like when coasting and slowing down.BTW- the idle is supposed to hang when the clutch pedal is down or the shifter is in neutral,when the car is slowing down for a stop or shifting.This is because of the idle dashpot function.I suppose if you want to cut the high idle off a little earlier than what the ECU is commanding it to do,the restrictor plate could be used.The plate supposedly reduces the airflow to cut the idle hangup off quicker.The following description is listed for a plate on Ebay.
** This IAC Restrictor Plate restricts the incoming air to the motor between shifting, and going into neutral getting rid of that RPM hang up.Drops that RPM hang up with (2) size Restrictor holes you can custom tune how fast you want the RPM to drop**

If you wanted to try the restrictor plate method,you could make one of them with a thin piece of sheet metal.Just set your iac valve on top of a piece of it,trace its outer flange shape and its mounting holes onto the metal,then cut it out with tin snips and drill the mounting holes.Then drill two different sized holes,in whatever diameter is shown or listed in an ad for one of these plates,then mount it and try it out.

The iac adjuster plate is different in its shape and function.Its used to increase idle a controlled/precise amount if the throttle body is built up with crud or if a rough/low idle is occurring due to a aftermarket cam and it can also cut bypass air off to lower idle too.
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1991 Mustang lx
D.S.S. 342ci {10.5:1}
TFS 190cc + track heat
Lunati 61011 .549".565"
Pro-M 76mm maf
Jetronic 30lb inj
QA1 Coilovers
17" Weld ProStar XP's
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Originally Posted by 90lxwhite View Post
Also how about the “restrictor plates.” The ones with two smaller holes in them that block the air. Are those supposed to do the same thing as the “adjuster” except ones adjustable and the other isn’t? Or are they two different animals?

I dont have any experience with the use of a restrictor plate,but going by the image & reading its description,its main purpose appears to be for the prevention/reduction of a hanging idle that occurs between shifts & when in neutral,like when coasting and slowing down.BTW- the idle is supposed to hang when the clutch pedal is down or the shifter is in neutral,when the car is slowing down for a stop or shifting.This is because of the idle dashpot function.I suppose if you want to cut the high idle off a little earlier than what the ECU is commanding it to do,the restrictor plate could be used.The plate supposedly reduces the airflow to cut the idle hangup off quicker.The following description is listed for a plate on Ebay.
** This IAC Restrictor Plate restricts the incoming air to the motor between shifting, and going into neutral getting rid of that RPM hang up.Drops that RPM hang up with (2) size Restrictor holes you can custom tune how fast you want the RPM to drop**

If you wanted to try the restrictor plate method,you could make one of them with a thin piece of sheet metal.Just set your iac valve on top of a piece of it,trace its outer flange shape and its mounting holes onto the metal,then cut it out with tin snips and drill the mounting holes.Then drill two different sized holes,in whatever diameter is shown or listed in an ad for one of these plates,then mount it and try it out.

The iac adjuster plate is different in its shape and function.Its used to increase idle a controlled/precise amount if the throttle body is built up with crud or if a rough/low idle is occurring due to a aftermarket cam and it can also cut bypass air off to lower idle too.
I see. So I believe the restrictor plate isn’t for me then.
Thanks homie.
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I see. So I believe the restrictor plate isn’t for me then.
Thanks homie.
Yeah according to how that part is made (with one small & one large hole) it can only bring idle back down and it does so quickly, depending on how its mounted.You can orientate it with the large passage over the clean air passage on the throttle body or the small passage over the clean air passage.


1991 Mustang lx
D.S.S. 342ci {10.5:1}
TFS 190cc + track heat
Lunati 61011 .549".565"
Pro-M 76mm maf
Jetronic 30lb inj
QA1 Coilovers
17" Weld ProStar XP's
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