Three weeks ago I did a tune up on my 89 5.0. New cap and rotor, 9MM Motorcraft plug wires and Motorcraft plugs. A few days after I started to have idling issues. Thinking it was probably something with the recent changes I had made, I started watching videos and reading forums for suggestions. This is what I did: AIC, cleaned original, then replace with new Plugs X 2 Cap & rotor X 2 Inspected for Vacuum leaks and sprayed engine with carburetor cleaner Replaced 02 upstream sensor Seafoam added to vacuum,oil and gas Mass air flow sensor tested and cleaned Test and cleaned EGR valve and EGR spacer openings (both were very dirty) Replaced coolant temperature sensor Replaced air charge temperature sensor Checked and reset timing (had to buy timing light) Tested TPS sensor with OHM meter Today I found the problem. It was a small vacuum line way up under the upper intake that goes to the charcoal canister, which is located in front of the passengers side fender. It was dry rotted at the nipple on the upper intake, which is virtually impossible to see without a lot of bending and a very bright light. I actually found it by trying a trick I saw on the Scotty Kilmer channel. I removed the vacuum line from the brake booster and blew lots of cigar smoke through the vacuum system which revealed where the leak was. So after spending $300 on parts and cleaners, a $5.00 vacuum line and a .50 cigar was the fix. I'm just dumping this here in the hope it will help someone else in the future.

Nice car, have a 1986 5.0 5 speed , t tops , stock ,2 1/2 inch exhaust,373 gears, and always runs great and does same as yours sometimes , never figured it out, and always idle at 1000 rpms,never below that, good luck.

Hey Bro, I noticed in your video that the charging gauge was not showing a positive charge at all, that in itself would cause the issues you speak of. Your electrical system needs over 12.5 to 14.0 volts to operate correctly.

Sounds like a simple fix. Check your Throttle Position Sensor and your IAC. If your TPS voltage is off at all it can reek havoc on your motor at lights. Please do us a favor and let us know what you found.

I know I am late to the party but I can tell everyone with 100% certainty what is wrong with everybody's car in this thread!! Everyone in this thread is telling everyone else what to replace because they had the same issue!! FYI the same issue can have different causes! Instead of just blabbering off parts to replace, Try spending a little extra time and learn how to actually diagnose these problems with these cars! They are extremely easy to work on with common hand tools! Instead of asking what is wrong with your cars you should ask how to diagnose the issue! You will save a ton of money and then you can go buy more tools for the next time!! Enjoy lol

Lower Intake gasket leak. Or maybe vacuum hose on the under side of the upper intake. Trust me bro I'm a doctor.

Bad TFI module , i had the same issues, $30-60 fix

I had the same problem with mine lol. After 200 plus dollars later found out it was an upper intake leak.

same here with my 95 GT. randomly stalling out as if it has lack of fuel. always happends when it's hot outside, 1/4 tank of gas. just yesterday it stalled with a full tank of gas. every ignition component has been replaced, so either it's a fuel issue, electrical or thermal issue. out of all the thousands of ppl that have had this issue everybody fixed it in a different way.

Replace the TPS! It is holding the EGR open and causing a lean mixture. Disconnect the hose to the EGR and plug it. If it smooths out, replace the TPS.

This is an old video but if you have not solve this issue look at these things. Check and make sure your ECT is plugged in and make sure the wires are not damaged. The reason being looking at your gauges your battery volts is very low and your coolant temp gauge showing no temp readings and also your oil pressure gauge is dead as well. The electrical is in a series electrical system to the gauges on Fords. If the ECT is not hooked up the gauges will be dead.

clean the 10 pin connections behind the upper intake for the injector harness . its been fixing a lot of issues with these foxbody mustangs

My 92 mustang also idled rough and turned off at a stop after 30 minutes of driving so i replaced the ignition coil, tfi module, and cleaned the idle control valve, throttle body. It doesn't idle rough or turn off anymore, but it misfires loud. I wasn't able to time it without the light.

My 95 was doing this and it was my vacuum hoses, replaced them idle is now great, ac works better and cruise doesn't go off and on.

mine had similar symptoms after i swapped out the engine. Turned out the maf harness wasn't fully seated. clicked it in all the way and was perfect. a bad tfi module will show similar symptoms too. get one from auto zone, lifetime warranty because it will fail again.

These Mustangs have Speed Density also knows as "EFI". There is something call an IAC "Idle air control valve".. it's very easy to take off and clean. Once you do that turn your key on for thirty seconds and back off for thirty seconds. Do that 3X. Make sure to use something that will not harm electronics for cleaning. The real way to fix this problem is to switch to mass air, but that gets expensive.

There are several parameters/sensors that are monitored by the CPU and are Critical for proper Idle Control. One problem I noticed, your idle when engine Hot was a little to high 1000 RPMs ? Should be closer 750 RPM at Hot idle. You may want to check and confirm your Base Idle Adjustment. Idle control can be affected by the MAF, TPS, O2 and ECT sensors. I would also say your MAP sensor but this vehicle is not and '86 and anything other than '86 is MAF controlled. Of course engine needs to checked when Hot, closed loop condition. When the problem is occurring I would monitor all the Sensors mentioned with an Scope , check them against the sensor charts to know what they should be reading. Also, do a OBD 1 system check, Key On Engine Off for codes. My '86 GT was doing the same as what you have mentioned. Turned out to be a bad ECT sensor, was indicating Cold when engine was Hot and adding Tons of fuel to the fuel injectors which in turn stalled the engine. Also if you suspect an Idle Control problem make sure you clean IAC and monitor also with a Scope on the control side of the IAC motor, there should be ~ a 20% duty cycle when in idle.

@WhoSaidTyler Well once the car has stalled, I try to restart. As I restart it trys to get going but it putters. When I put the gas down to the floor, nothing happens. When I start and pump the gas as it starts to hit it will grumble a wee bit but still fail. It repeats this problem for about 20 times and then she will sputter and when I pump the gas she is off like a bandit. Its very odd.

What did the problem turn out to be?

Looks like u need a battery first off .. If it gets hot/warm then shuts off or won't start when warm/hot, it could be your ignition control module which is attach to the distributor cap.. Change it or go have it tested and I bet your problem is fixed.. Looks nice and clean... I like it..

Idle is a tad high, In my expert opinion. I believe u have a vacuum leak. I would trace it under intake to tree and cansiter. Remove upper intake. Also IAC would be my second spot to hunt. I drilled and ohmed tps to close to .99.

Tyler, Yeah, that was the first thing the mechanic did. He pulled the small advance plug at the base of the dist. They then timed it and put the plug back in. The funny thing is I can remember it doing this to me once before (prior to timing it) You don't think it could be a vacuum issue or idle air control motor, do you?

for one your battery is reading low and its probably your vacuum lines. Charge your battery and check all of your vacuum lines going to the throttle body

Adjust your throttle position sensor. Use a digital meter put the neg to the ground strap in the pass side firewall set the meter to DC then put the pos lead to the green wire on the TPS adjust with the two screws on top turn till you get the meter to read between .920 to .950, .960

i heard that you ran over your ladder. oops. i had this problem with after market cams in 5.0s even with mass air. ecm doesnt like different cams. factory cam isnt a bad piece but the intake and heads arent great.

@OhYeahAboutThat I am in Odessa, Originally I purchased the car from a guy in Tampa near Race Track Rd.

The Pcm requires constant voltage usually 13.2-13.6 can not and will not run properly with low voltage due to a failing battery or alternater I say this only because when watching the video towards the end the battery or charging gauge was all the way down in the red close to 8.... It could be the gauge just not accurate but I would start with charging system test.

I’m having the same issue with my 91 cannot figure it out

Hmmm...when you checked the timing, did you pull the SPOUT plug out? The spout plug is a gray piece of plastic which plugs into the harness a few inches to the driver side of the distributor. When removed it reverts the timing back down to base timing without the computer trying to control it. Past that might be a fuel pump getting weak. What's with the gauges not working?

Watch for 10 minutes and there was only one problem... you ran over your ladder. lol

Noticed your guages seem to be not working correctly. The symptoms you are having can be caused by a poor ground connection from your motor to the car itself. My '71 Mustang had the same problems until I repaired the ground cable.

FOR MANY YEARS NOW I HAVE HAD IDLE PROBLEMS FROM CAR DYING WHEN AIR COND. IS ON TO HIGH IDLE WHEN CAR IS IN NEUTRAL AT 1,500+ RPMS. HAVE CLEANED THROTTLE BODY, CLEANED IAC, REPLACED BOTH SENSORS ECT AND ACT? ALSO REPLACED IAC. IT'S CHRONIC.

Check your cold idle vacuum tube relay transmitter located near your catalytic repeater

Yeah if its not vacuum then I guess TPS or TFI module.

Since the O2 sensors take a while to heat up the car would start good. Then after taking off n a few minutes later it would run like crap, and that's cause the O2 sensors get into operating temperature. The reason the car would run good while flooring it is cause the O2 sensors r bypassed while flirting it. So in my case after changing the O2s my car runs good now.

He might have underdrive pulleys installed. I had a set installed in my old 5.0 and had the same result. Idle was the same after sitting for a few minutes. Add in a couple mods. Electric fans,stereo etc.. It doesn't do the battery any good. At cruising speeds the alternator works fine is my guess.

Bad capacitor in computer or loose ground...

That is a very nice fox you have there. You more than likely have this issue fixed since this was posted in 2011 but my guess would be if it does it when it warms up, could be the TFS module on the distributor, those have a tendency to go out like that.

Bad tps to me. Noticed you hit the throttle and the rpms stayed up. Gotta be tps. Either adjust or replace.

It's your ignition switch the wiring harness on the steering column check it out

Where you able to figure it out because a customers car did the same thing and it was vaccum lines for the map sensor

Get a idle air adjuster plate from LMR.

Hi archifxllc! I have a fox body 91" that is doing the same thing. Did you figured out what was your problem? Please if you did help me out.

@archifxllc What's it do if you try to just gas it and drive away while it's having one of these fits?

Have you cleaned the idol control solenoid valve on the throttle body?

Just my two cents but that BBK throttle body should have coolant running through it, and you can go to autozone or napa and pick up an obd 1 scan tool for ten bucks it plugs into a service port in the engine compartment, also check your MAP sensor. My 90 was stalling intermittently and that was the problem. It's on the firewall just to the left of the vacuum cluster. Hopefully you have figured it out already but if not hope this helps.

My ol' ladys 95' is having an issue like this one. She idles at 2k but putts then soon stalls. When fired again, it holds the idle then stalls especially when put into gear. Ive replaced the TFI, Battery and Vacuum hoses. If anyone has a clue as to what may be the issue please let me know. Im sure your answer will also help this guy as well (if hes still workin on his car) thank you

did you ever get your problem soved??? had this kind of issue before ending up being a bad fuel pump. hope you got it figured out

Did he ever fix the problem 🤔

hot tfi module or like they said pip. replace them both or a new dizzy. and also replace both 02 sensors. mine did the same exact thing. and for grind into reverse put it in 2nd then into reverse or blow ur t5 up and get a t5z like I did lol j/p. that is a mass air car so clean the sensor with a qtip VERY carefully. very nice ride man. I have a 90 lx hatch sunroof car with the same wheels. love the car. keep in touch via email with ur issues. ive been all over this car and got pretty good at fixing these puppies. good luck

Noticed that it isn't charging either, may have something to do with it getting weak fire when warm.

I also had the same problem, and found out it was the fuel pump. It didn't do it while idling only when I was driving.

Be happy, I have the same thing but mine does idle like yours...

I've got one in my boat if i turn it off after hours running motor won't start till engine is cold ...have replaced the tfi module...still having starting issues when hot ..ive got 3 batterys so there plenty of current to preform starting ..but won't fire

Did you fix your gauges yet?

look at the volt gauge your alternator is shot and there for your motor will run and then run like crap and electrical lights will flash and come on until the battery is completely dead and the car wont run off the battery

If the EEC V don't get propper 13 to 14v it will cause all kinds of driveability issues. Also the computer looks at the ECT for engine temp so it can determine open loop vs closed loop.

IS YOUR BATTERY GAUGE AND TEMP GAUGE NOT WORKING? MY FUEL GAUGE WILL GO PAST FULL AND STICK THAT WAY EVEN WHEN CAR IS EMPTY THEN IT WILL RETURN TO NORMAL. EXPECT THE IDLE PROBLEM WILL NOT APPEAR WHEN YOU SHOW PROBLEM TO MECHANIC OR ANYONE. I HAVE GONE THOUGH THIS FOR YEARS. LOTS OF OLD CAR PROBLEMS LIKE BROKEN VAC. LINES.

Hello do you know what's the problem was i have the same problem with my foxbody

I have a high output 302 in a 59 Ford Custom 300 and it stalls whenever I come to a stop, could it possibly be the idle?

I have the same problem, 1988 5.0 lx and the battery gauge is always right by the red, then it drops down to about 500rpm and stalls. I replace the alternator and it did NOT fix the problem.

Did you ever check your TFI module? I had a problem with that once the engine warmed up. IAC shouldn't be a problem considering that she started right up and idled perfectly. Listen for vacuum leaks, ensure wires, ignition coil, and tfi are in good condition (anything funky with the tach before it dies is a good indicator for tfi failure, it has a tach wire). Test fuel pump pressure after long operation... And I mean other than that you don't have much left. If you're a decent electrician, go through your engine harness like I did. Found stuff that shouldn't be there, broken wires, frayed wires, etc. These are all personal experiences I've had with my 88 5.0 which I DD to work.

i have that problem now with my 94 i know the mass air flow meter is bad so its unplugged for now but when my car gets hot it stalls out and wont start until its cooled down

I had a similar problem. Would start up then after a few minutes of driving, it would start to surge, buckle, missfire. Oddly enough if u would floor it with this symptoms, it would start to run fine(wile flooring it) this led me realize I had bad O2 sensors

I think you may need a new alternator and or battery or both your voltage should be at 13.2 to 14.2 volts when running and charging right I would load test that battery and do a voltage output test and amp test on your alternator advance auto and AutoZone will test both of them for free good luck I hope you get your mustang fixed nice car man

Can't get codes for those cars anymore but did is right about the voltage and oil marker bad alternator? Oil pump? My car was revving and bogging nd would turn off at stop lights every once in a while due to bad/weak alternator

I have the same exact problem with my 95 gt. Did you figure it out? i really want to get mine fixed i just bought it. Thanks

Sounds like you have open wires hitting something pop in the fuse used to happen in my old truck pop the same fuse ended up being around the exhaust

i can hear the typical loud fox power steering pump, and the clutch grind when you put it into reverse, shitty t-5's... my fox did the same exact thing.

same problem with my bronco two 86 cleaned out the throttle body still does it

Are all of your gauges working? because if your running off of your battery it will cause the same kind of issues,,,

Is the volt meter gauge not work? You could have a bad ground or alt is out.

did you take a look at the tps to see if it is positioned right.

Looks like you need a new alternator clean out the mass air idle sensor check your TPI rubber hoses

i had my engine rebuilt and i have a feeling mine is doing the same thing ... i have to put it in N or park so it doesnt want to try to die at lights now although its throwing codes of lean on both banks at o2 sensor i think maybe il have the timing checked as the ass that rebuilt the engine says its perfectly fine ... if it was i wouldnt be haven problems

Put new 02 sensors in it, stopped my bucking and bad idle, also look for an intake leak,pcv,where upper meets lower manifold, check your altenator,you need a new one

I see the battery gauge is in the red(not charging), it should be in the middle... and the heat gauge isnt reading either?..it should be 1/2 too.

Hey, I really like that car. Seems like it may be vacuum related. I sent you a PM a while back. I'm in Tampa and would love to hear back.

so? what was wring with it?

T- tops!!!! I dont see that very often!!!

Beautiful car !!

Pull the clip when timed?

check you IAC could be clogged up

Saw that at the 8 minute mark in the video

❓❓❓❓So what was it❓❓❓

i'm having the same problem with my 1990 new yorker and the people bring it to can't seem to figure out whats wrong with it. did you figure it out?

what did yall set the timing to?

does you volt gauge work because its in the red you should have 12 to 14 volts not 8

It should be at 13.5 while running yours is sitting at 9 unless you know that gauge is F up touch the brake pedal it should shut off then

TPS or IAC

Low battery and no oil pressure weird.

replace the o2 sensor EGR if it has then replace the spark plug wires and plugs then last but not least the fuel regulator lol maybe that would help I have an ford windstar that did this and that's what I am stuck with get all the codes read and good luck

is your alternator working??

Unless it's originally a California car, which got mass air for the '88 model.

So did anyone figure out what the problem was by any chance??

Don't feel bad my rear end locked into positive traction and I didn't do it I guess if that's were it wants to be guess I just just leave it there

T-top sick fox bro..hope you got issue resolved

Had the same shit happen to me last week. Would turn on and off intermittently while driving, idled like shit and then when it finally went out it wouldn't start at all. Turned out to be the fuel pump relay. Always keep a spare TFI module and fuel pump relay in your glove box. Also, the inertia switch could be acting up. I'm pretty sure you've already figured this out because the vid is old as fuck but for others here in 2019, these are some possible solutions.

Just noticed this is like 2 yrs. Old but ur idle is too high, you should be 600 to 800 i believe more around 800, looks like a nice ride hope u finaly figured it out. If so what was it? Because I have one and its just started doing it also, not dying but idle high.

Also no oil pressure and the car sounds funny