[Gallie]

Here's the deal:

1991 Mustang 5.0 LX. 180K, original owner and all stock.

I've replaced the following:

- Right and left oxygen sensors
- EGR valve
- TAD and TAB Solenoids (both Thermactor air bypass solenoids)
- IAB valve
- ECT Sensor
- ACT Sensor
- Coolant temp sender

I've also:

- Adjusted the TPS to various ranges from .99 to .90
- Checked spark plugs to factory gap
- Adjusted the timing
- I've checked the codes both with engine off and on and all the engine codes are fine (Code 11 - system pass).

After all that here's the symptom that has continued through all these:

The car starts and idles perfect...right on spec. This can last for my entire ride into work (40 minutes) and still OK.

Then all of a sudden, usually after sitting with the car in gear and idling...it will stall. The car dies and upon start up, it idles rough....LIKE CRAP.

If I drive it at highway speed then come to a stop it idles good again. Then after sitting there it does the same thing.

I'm ready to dynamite my car!!

I've got the match lit...can anyone help me from blowing up my car!!!

Thanks,

Gallie

[onehot351]

sounds like your car is gettin to much fuel and is flooding out at idle

[Gallie]

Is it too much or too little fuel?

What makes you think it's too much...is it because it stalls out as it sits longer?

What do you think it is?

Since I've replaced/checked a whole lot....how about the MAF?

Could the TPS be going bad?

Oh, I also forgot to mention that I changed the TFI, Ignition module, too.

[Gallie]

Any thoughts..anyone.

[dr.gonzo!]

That sounds like what mine is doing. I noticed my voltage drops really bad when its about to stall but The guy who owned it before installed underdrive pulleys and I have heard that the stock alternater is not really putting the juice out it needs to and the U/D pulleys make it worse. Mine works fine when its cold outside though so it is weird. And I dont think it is flooding if your car is Fuel injected.

What brand did you go with on your ignition module? I went with the cheap on from autozone but I am thinking about steping up to an accel module.

[nitrouskid]

my friend had that same problem with his 88 it would be fine when it first started and when it was cold and then when it was up to temp and just left idling it would stall he to replaced a lot of things and it just ended up being an intake gasket

[dr.gonzo!]

where at on the intake?

[Gallie]

I went with the cheap Autozone ignition module for $38.

My car does seem to be running better, but it's still got that intermittent stall/rough idle.

I'm confused why the intake leak would cause this to happen intermittently and not continually.

Thanks,

Gallie

[dr.gonzo!]

Because of the heating and expanding the hole in the gasket and allowing air to get in.

[2007calispecial]

try doing a tune up it could probobly use it and will maybe fix your problem, Cap and rotor, spark plugs, make sure your intake is not dirty/clogged..

[dr.gonzo!]

I did that about 3 weeks ago. still fine in the cool morning then runs like shit on the way home in the afternoon.

[Gallie]

Just thinking... :wink

You mentioned the voltage drops. I noticed mine does that too when it begins running rough, but I just figured it was because the idle drops.

Do you think it could be the other way around?...the voltage is causing the idle to drop??

Help me out, anyone, how about the voltage regulator...would that produce this kind of problem and how would one test it.

Gallie

[Ttop]

If you have acsess to a fuel pressure tester, check you fuel pressure first. I've seen pumps that will start to go bad and loose pressure at an idle, worn out pump + low system voltage at an idle from the underdrive pullys could = low fuel pressure. I think KOEO is 35-40 psi and KOER is 30-35, don't remember off the top of my head. If so replace the pump and filter. As far as the intake goes, the gaskets could be leaking vacume under the intake. About a year ago I had a Mustang come in the shop with similar problems. I checked for everything, vacume leaks, dirty MAF, bad IAC, EGR, O2s, ect. Couldn't find any problems. So after 3 hours of free diag, (commission work sucks sometimes ) I pulled the intake and found 2 felpro gaskets stuck together on each side of the intake . Once the eng. was fully warmed up it would crate a vacume leak under the intake just big enough that it would run bad at an idle. It had a cam, heads, a cobra intake, headers, and a catback so it ran ok of idle. Higher mileage engs. can form intake leaks due to the repeted heat cycle ,or, warming up and cooling down of the eng., causing the gasket to basicaly fall apart. Sorry for the long post. Hope that helps.

[the tick]

have the e303 cam which makes mine idle rough and i noticed the voltage drops when the idle drops so i think its theidle causing the low voltage

[Gallie]

I adusted the TPS to .99 and made sure the timing was on 10 degrees BTC. Interesting though...

If I check the timing with that little grey plug attached, the timing is erradic. The timing mark jumps all over. Once I remove the plug the timing seems consistent and the car seems to idle better.

Can anyone tell me more about that little grey plug that you remove when you set the timing? What does it do?

Thanks,

Gallie

[the tick]

that grey plug is what lets your car adjust the timing under acceleration rev it up when that plug is out it will run rough i beleieve atleast my understanding

[IcantDo55]

Originally Posted by Gallie I adusted the TPS to .99 and made sure the timing was on 10 degrees BTC. Interesting though... If I check the timing with that little grey plug attached, the timing is erradic. The timing mark jumps all over. Once I remove the plug the timing seems consistent and the car seems to idle better. Can anyone tell me more about that little grey plug that you remove when you set the timing? What does it do? Thanks, Gallie

It eliminates the computer advance (16* to 20* depending on the computer).
If you think you are on to something in the timing set the timing for 34* with the connector out and leave it out and try driving it. It will keep the computer from adding timing. I done thin on SC cars to keep the stock computer from adding too much timing when under boost.