Fixing your SURGING IDLE!!! IN HERE!!!

Widow Maker · Feb 23, 2012

Love this thread

Locomoco · Jun 8, 2012

This thread has a lot of information. Eventho I run a automotive repair shop I was having a idle surge issue as well, late last night I was on here reading and I have to say good information and important info as well. So anyways I went to work today with the idea I was going to follow the steps in the link that was provided. And on the way to work this morning looking at my fuel trim I was running FAT and started thinking to myself no wonder I have idle surge issues, so after I get there I turn my battery off because I'm cool like that lol so to make this story longer I started by taking my strut brace off to allow access to my throttle body. So I started with removing my iac motor to check for carbon, next I pulled the tps just because I can wanted to make sure it was in the correct setting, next I pulled the maf and cleaned the hot wire, anyways I made a change I changed all parts with factory parts, next I said well hey this morning you were running really fat and made a choice to adjust my bbk adjustable fuel pressure regulator, after getting the darn thing running I pulled the vacuum line off the regulator and to my surprise the regulator was peeing fuel lol DING DING the bells go off in my head no wonder why lol so I call my local ford dealership and talk to my man I know in parts very well and order a stock regulator. Put it all back together and you know what my car runs awesome again. Just wanted to say thanks everyone for posting up info on idle surge if it wasn't for you guys I would have just let it go for a bit longer. I even got a megasquirt because I was thinking it had to do with open and closed loop and it didn't. I am going to order a new regulator from bbk because I like there product but bottom line reason for the post is because no one talked about the fuel pressure regulator and wanted to put some new info for others to just check when they are doing all them step.

Addermk2 · Jun 8, 2012

I've posted numerous times that idle surging is caused by excessively rich idle fuel trims. But everyone would rather slap a bandaid on, instead of fixing their cars.

#1 culprit: O2 sensors
#2: ECT/IAT sensor
#3: being told by some jackass, that you need to pump your fuel pressure to make more power...

Smh

Locomoco · Jun 9, 2012

Addermk2 said:
I've posted numerous times that idle surging is caused by excessively rich idle fuel trims. But everyone would rather slap a bandaid on, instead of fixing their cars.

#1 culprit: O2 sensors
#2: ECT/IAT sensor
#3: being told by some jackass, that you need to pump your fuel pressure to make more power...

Smh

Yeah pumping your fuel pressure is just a bandaid fix. Being able to truly fix your problem is priceless

the funny thing about this is a fellow co-worker is really big into mustangs and he was the one to pump mine up. And his fix for the problem was new ecu or chip would only be the way to fix it. Me being a tech by trade I knew there was something else that was the cause. Kind of funny IMO

Ferocious · Jun 9, 2012

I did every step from the muscularmustangs write-up on my 4.6 the other day and wow. What a difference it made.

89stallion · Jul 5, 2012

Excellent info.thanks

backwater309 · Aug 10, 2012

95_vert302:
distributor

Fast stang16 · Jan 27, 2015

dsg gts said:
ok now the idle is worked out. now new problem.after i first start it say the first 5 min. it will rip up any road. then it starts to run strange. it misses then it straightens out runs good not great but ok. then it stumbles real bad almost wants to shut down i give it lots of gas to keep it running. the it throws a check engine light. reves up to 2500 then it settles down to normal. this whole process takes from 10 to 15 mins.then it runs fine except for the steady driving. i can speed up fine and slow down ok but a steady cruise it misses or bucks.i've replaced every sensor. every vacumn area. even sprayed the intrie intake up over around searching for a leak nothing. could the distributor be the problem? how would i check that?

Did you ever figure out what this problem was? My car is doing the same thing!

lutter94 · Jan 27, 2015

Locomoco said:
This thread has a lot of information. Eventho I run a automotive repair shop I was having a idle surge issue as well, late last night I was on here reading and I have to say good information and important info as well. So anyways I went to work today with the idea I was going to follow the steps in the link that was provided. And on the way to work this morning looking at my fuel trim I was running FAT and started thinking to myself no wonder I have idle surge issues, so after I get there I turn my battery off because I'm cool like that lol so to make this story longer I started by taking my strut brace off to allow access to my throttle body. So I started with removing my iac motor to check for carbon, next I pulled the tps just because I can wanted to make sure it was in the correct setting, next I pulled the maf and cleaned the hot wire, anyways I made a change I changed all parts with factory parts, next I said well hey this morning you were running really fat and made a choice to adjust my bbk adjustable fuel pressure regulator, after getting the darn thing running I pulled the vacuum line off the regulator and to my surprise the regulator was peeing fuel lol DING DING the bells go off in my head no wonder why lol so I call my local ford dealership and talk to my man I know in parts very well and order a stock regulator. Put it all back together and you know what my car runs awesome again. Just wanted to say thanks everyone for posting up info on idle surge if it wasn't for you guys I would have just let it go for a bit longer. I even got a megasquirt because I was thinking it had to do with open and closed loop and it didn't. I am going to order a new regulator from bbk because I like there product but bottom line reason for the post is because no one talked about the fuel pressure regulator and wanted to put some new info for others to just check when they are doing all them step.

This. Was. Painful. To. Read.

RustangJeeTee · Jan 12, 2016

Mine surges sometime, but it also likes to stall when I push the clutch in. It doesn't do it all the time, but when it does, it's a pain in the ass.

Bdons_95gt · Jun 13, 2016

I'm so glad I found this stickie. I browse on Tapatalk so they don't just pop up at the top like a browser. Anyway, I was having tons of the typical stalling issues, I went through EVERYTHING. New distributor, ignition module, ignition coil, iac valve, MAF sensor etc.. It still sounded like it was loping while hovering around 500 rpm at idle and it would stall once I awhile while coming to a stop. Adjusted the base idle and the tps, I'm 250 miles in without an issue! I have no doubt everything I changed out needed it since it was all factory. I think when the PO installed the bbk throttle body he adjusted the base idle with a bad iac valve, how he managed it I don't know, but it's running great now!!

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smittysweet · Aug 20, 2017

ok I see it says fixing your surging idle but what about stuck idle my 94 idles at 1700-2000 rpm and wont go down no mater what
now ive changed the tps the throttle body and iac the onley thing I can do is block iac and idle it up to normal but ide rather not do that
is there a place here I can get this problem figured out or is this not a commen problem I say again no surge just idle at 17-2000 rpm
also tps reads 1.4 volts when connected but when not connected to throttle body just in my hand it reads 0.95 any sugestions will be tried as I'm stuck on this
I have a 1994 mustang gt 5.0 with 5 speed trans onley mods are bbk 75mm tb and cold air intake mods where installed after problem started

smittysweet · Aug 20, 2017

https://www.facebook.com/groups/223899334775576/permalink/232982293867280/ this is what it does no mater how long or short it runs never changes

ttocs · Aug 23, 2017

you say the tps has two different measurements. have you adjusted the tps like it shows at about the 2 min mark here? This is a fox version but we do the same thing on ours.

[video=youtube;HUwr0g5Qn7s]https://www.youtube.com/watch?v=HUwr0g5Qn7s[/video]

ttocs · Aug 23, 2017

smittysweet said:
https://www.facebook.com/groups/223899334775576/permalink/232982293867280/ this is what it does no mater how long or short it runs never changes

This link just takes you to a facebook page about what is happening in anderson county.

akaNYr · Feb 18, 2019

95PONIES said:
I've built and owned at least ten mustangs all early 90's though and had zero driveability issues. This is my first sn95 I picked up couple months ago and about from the jump it stumbles down low, after chasing around the problem it got starting issues...ended up being the dizzy. Ok bout a week later I got the same surging I see alot of you have, checked everything, tps,cleaned IAC, cleaned maf,replaced maf, set base idle, adjusted set screw, tried a different ecm etc. etc. I was ready to burn the damn thing it would surge to 2000 rpm no matter what I did!!! :BangHead: I've been a tech for almost 15 years and now work for a large family owned auto salvage yard so I know how to track down issues but I almost lost it on this one!! Lol...today I'd had it my brakes were smoking by the time I got to work today as the rpm's reached 3000 today the whole 20 minute drive!! so me and an old timer from work did the most simple tests no scanner, no voltmeter, just used our hands, pulled intake tube started car covered throttle body died instantly, took off IAC motor started car covered that with hand car died so we eliminated the idea of a vacuum leak. So we ended up taking a pepsi can poking two holes in it with a test light trimed it to cover the hole closest to the front of the IAC and screwed her back down with IAC plugged in. fired her up and what would ya know ....she idles smoothly at about 700 rpms, doesnt stick,no more surge, nothing but a smooh idle!! A band aid fix I know but after three weeks and trying any and everything else all of you suggested, It will stay there until next year when I finish rebuilding my 4 valve for a turbo project I plan....did I mention no CEL either since the IAC is still plugged in. :headbang:

I know this is an old post but I'm going crazy withI'm about to fix it with a gallon of gas & a match. Can you please explain a bit more on the Pepsi can fix you did. Like how big holes where. How far apart are the holes. Trimed the Pepsi can to cover the hole closest to the front of the IAC? How did you position the Pepsi can to the IAC and then screw it back down? I've been trying every thing I read for 3 months to fix the surging.

ttocs · Feb 18, 2019

It varies on a lot of things, if you want to hit the easy button get this.

https://lmr.com/item/LRS-9939A/1986...H-_o0cVwjsmkKruD2tyKHNnWLa-oyfoQaAmC4EALw_wcB

Werecow · Feb 10, 2020

Just my $0.02 on this one.. in doing the troubleshooting steps for this issue on the 94 5.0 I'm working on now, when I got it, it had the same surging issue some of you have battles here. I found one of the vacuum lines under the upper intake manifold plenum was completely disconnected. I couldn't get to it to put a plug on it without taking it off so I used a hose which worked out well because then I had somewhere to hook up a vacuum gauge. It still acted like it had a leak somewhere else, and when I took the IAC valve off to clean it, not only was the gasket in pieces but the body had a crack in it as well. So right there was not only an external vacuum leak, but the IAC valve couldn't do its job because of the leak inside of it.. so all the adjustment in the world was useless on it because of an internal crack. Lesson here.. just cause it still looks pretty don't mean it's doing its job... And as several ppl have pointed out here before vacuum leaks can be the easiest and the hardest things to miss.. look in YouTube for smoke chimneys if you wanna find vacuum leaks that you can't seem to track down.. O2 sensors are another thing that can throw off everything.. I know mine are bad still but that's why mine's running pig fat right now. And as far as the one that was dying when you turned the steering wheel? If I remember isn't there a pressure sensor in the steering system somehow that will work with the computer that's supposed to adjust the throttle when the the steering system needs more input from the engine? I seem to remember part of the testing thing when you hook up a code reader that turning the steering wheel is part of getting some series of tests done? I may be waaaaaaaaayyyy out in left field on this, if I am call me an idiot.. anyhooo... That's my $0.02 cheers mates!!

Callmety24 · Jan 28, 2021

Werecow said:
Just my $0.02 on this one.. in doing the troubleshooting steps for this issue on the 94 5.0 I'm working on now, when I got it, it had the same surging issue some of you have battles here. I found one of the vacuum lines under the upper intake manifold plenum was completely disconnected. I couldn't get to it to put a plug on it without taking it off so I used a hose which worked out well because then I had somewhere to hook up a vacuum gauge. It still acted like it had a leak somewhere else, and when I took the IAC valve off to clean it, not only was the gasket in pieces but the body had a crack in it as well. So right there was not only an external vacuum leak, but the IAC valve couldn't do its job because of the leak inside of it.. so all the adjustment in the world was useless on it because of an internal crack. Lesson here.. just cause it still looks pretty don't mean it's doing its job... And as several ppl have pointed out here before vacuum leaks can be the easiest and the hardest things to miss.. look in YouTube for smoke chimneys if you wanna find vacuum leaks that you can't seem to track down.. O2 sensors are another thing that can throw off everything.. I know mine are bad still but that's why mine's running pig fat right now. And as far as the one that was dying when you turned the steering wheel? If I remember isn't there a pressure sensor in the steering system somehow that will work with the computer that's supposed to adjust the throttle when the the steering system needs more input from the engine? I seem to remember part of the testing thing when you hook up a code reader that turning the steering wheel is part of getting some series of tests done? I may be waaaaaaaaayyyy out in left field on this, if I am call me an idiot.. anyhooo... That's my $0.02 cheers mates!!

This helped me alot. Thank you sir [emoji120]

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Knightstallion · Jul 8, 2021

95gtdrop said:
its good to know that other people have the same problems.
i really would like to know if it is the iac that needs to be replaced.
i am looking for a permanent answer!
my carwill sometimes die on me three times in a row as well.
other days it wont have any problems. some tiems weeks at a time.

It's not just you I'm still working on this problem since it started on my sn95 over a year ago, we'd replace something thinking that was it and it would run about a week or 2, then do the exact same thing again, I'm currently working on checking wiring and timing, I recently read that having an aftermarket distributor was causing a couple people's problems on their 95 gt's and at some point a mechanic had replaced the pickup coil with a motorcraft pickup fixed it. Even to the point that some people were buying msd distributors and gutting them and putting motorcraft parts inside to get the look but have a running vehicle, I'm having trouble finding a store that carries motorcraft parts