Cant figure out problem??? 87 5.0

I hope you have enough gas in the car. and for it to stall under hard breaking like that is unusal. if you are accelerating (motor needs to be loaded) and let off and imediatly put it in nuetral will it die then? if it does then it sounds like the idle air control valve is broken

not sure if my experience is related, but i was sometimes stalling when i came to a stop, but only when downshifting, and then puting it into neutral, and it only happened every once and a while. CEL would come on then it would die. pulled some codes, MAF voltage too low, EGR not operating properly. i clocked my MAF meter (spun it around) , and for the last two weeks, no more CEL, and no more stalling.

when you did the conversion, did you splice into the vehicle speed sensor harness? if not that has been the cause of some stalling problems.

What kind of vacuum signal reading do you have? If you have a SD friendly set-up still (even though you have the conversion), you should see nearly 20" hg at idle.

It sounds like you have a vac leak, plain and simple.

I dont see the TAB/TAD causing your issue. Just make sure the vac lines and connections are tight/sealed.
Good luck.

See "Surging Idle Checklist for help with all your idle problems. The first two posts contain all the updates to the fixes. I continue to update it as more people post fixes or ask questions.

fourmustangs said:

nah I didnt.........where is that located and what do I need to do?????


also
I think it might be the Thermactor air diverter and bypass solenoids....thats the only thing left to replace on mine that would cause this......

plus I pulled codes 81 + 82

Click to expand...

those solonoids won't make a difference in the way your car runs. I've had them bypassed for a LONG time and have a tube going straight from the smog pump to the H pipe.

I'm kinda thinking it's an internal leak in the booster itself. Unplug the brake booster and block off the line, go out and drive it and pump your brake HARD and see if it dies.

be careful you'll have a VERY stiff brake pedal, but's it's driveable, I drove without a brake booster for 2-3 months.

also, on that explorer intake, some of them have two fake/dead vacuum ports coming off of the front of them on the front of the upper. Before you bolt the intake down, be sure that all of the intake ports are clear and open

Check the inertia switch in the trunk, maybe faulty.

did you read my post?? tab/tad solonoids won't make a damn difference in the world. All those do is switch smog pump air to the heads when cold, then to the cats when warm. Won't effect the way it runs at all.

automatic?

IS THIS 5SPD OR AUTO? CHECK THE TORQUE CONVERRTER IF AUTOMATIC

I'm gonna agree that you probably have a bad brake booster. I had one go bad in my 84' and just about killed the car every time I hit the brakes until I got home. Did you say you turned the fuel pressure down to 20psi? Stock is 37-39 and setting that as low as 20 would cause your injectors to dribble more than flow causing some other issues.

Good troubleshooting takes time. Everyone seems to be looking for
the magic tip that says replace this $13 part and your problems are
cured. You don't have to think, dig or diagnose, just buy the part and
install it. Unfortunately, it doesn’t work that way 99% of the time.
Thinking is hard work and educated thinking requires much more
effort than simple parts swapping. The complexity and age of these
5.0 Mustangs works against that, as well as the number of hands
that have “modified” the original design. Sometimes that
modification is well done with good workmanship and other times it
is mechanical road kill. It is very easy to become the victim of the
previous owner’s efforts.

I spend a great deal of time trying to communicate the methodology
of structured troubleshooting principles. For those who haven’t been
beaten with this stick before, here they are again:

1.) Understand the system. That involves reading some books to get
an overall picture of how it works. For 5.0 Mustangs, that list starts
with the Chilton shop manual and the Probst book, Ford Fuel
Injection & Electronic Engine Control 1988-1993 by Charles
Probst :ISBN 0-8376-0301-3. It's about $30 from Borders.com, see
http://www.amazon.com. Select books and then select
search. Use the ISBN number (without dashes or spaces) to do a
search. Use the ISBN number and your local library can get you a
loaner copy for free for 2 weeks or so. Another resource is the
following website by Tmoss (diagram designer) & Stang&2Birds
(website host) for help on 88-95 wiring:
http://www.veryuseful.com/mustang/tech/engine. Study
the diagrams and tech articles. There is an amazing amount of good
stuff in one place for FREE.

2.) Isolate the problem. You need to be able to break the system
down into functional blocks or subsystems. Once you know what
subsystem has failed, it is much easier to troubleshoot. Group
problem symptoms according to what system controls them. Don’t
look for a fix for ignition problems by adjusting the fuel pressure.
Have an organized, step by step, approach to work your way through
a subsystem and check its functions. Work all the way through a
subsystem before you quit and go off wildly chasing rabbits. You
have three tools to use in your efforts: measure, meter and
observe. Use these three tools to narrow down the list of possible
failure points into a small, easily managed list of items.

3.) Install the fix. .Now that you have a short list of suspected
villains, plan your repair efforts so that you do the easy things first.
If an item from the easy list didn’t fix your problem, then look at the
high failure rate items. Spend some time here on Stangnet and you’ll
get an idea of what the most commonly replaced parts are, things
like TFI modules, ignition switches and fuel pumps.

If you make a change and it doesn’t relieve the problem symptoms,
put it back the way it was. I have a stack of parts from where I
swapped a part and it didn’t fix the problem. I put the old part back
on the car and the new part went on the shelf. Someday I will either
use them or trade them for something else.