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1995 Mustang GT- Stalls @ Idle, Codes Present

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5.0L (1979-1995) Mustang Technical discussions on 5.0 Liter Mustangs within. This does not include the 5.0 from the 2011 Mustang GT. That information is in the 2005-1011 section.

1995 Mustang GT- Stalls @ Idle, Codes Present

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Old 05-16-2018, 08:08 PM
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Urambo Tauro
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Default 1995 Mustang GT- Stalls @ Idle, Codes Present

1995 Mustang GT, 178,000 miles

On my way home today, my '95 developed a nasty tendency to stall whenever I slowed to stop. It's got a T5 manual, but it didn't matter whether I was coasting in neutral, or holding the clutch disengaged. Without constant pressure on the accelerator, it would try to stall. I had to restart the car nearly a dozen times (good thing I have a good battery & charging system). Once restarted, the engine would idle roughly, around the 400RPM range. The car drove fine as long as there was pressure on the accelerator, but as soon as I'd lift my foot, the revs would rapidly start falling back down.

I had a hunch that there might be a problem with the IAC valve, so I thought I might try cleaning it once I got home. I stopped by the parts store for an IAC gasket, but they didn't have one in stock. Before I got home, I figured I'd try disconnecting the IAC plug, but the problem persisted the rest of the way.

Once I got home and changed my clothes, I went back out to the car, started it, plugged the IAC back in and heard the engine speed increase. But before going any further, I decided to check for stored codes. This is what I found:

KOEO- 113, 157, 212
KOER- 116

113 - ACT Sensor Circuit Above Maximum Voltage of 4.6 volts (O), ACT circuit has intermittently failed above the maximum of 4.6 volts (CM)
116 - ECT out of self test range 0.3 to 3.7 volts
157 - MAF sensor went below 0.4 volts during the last 80 warm-up cycles
212 - Loss of IDM (Ignition Diagnostic Monitor) input to EEC or SPOUT circuit grounded
Do I really need to chase these down one-at-a-time, or do you suppose these codes have something in common? I've got Ford's regular Service Manual, and the EVTM, but not the "Powertrain Control/Emissions Diagnosis" volume, so I'm not sure where would be the best place to start here.

Any ideas?
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Old 05-17-2018, 02:35 PM
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Did some poking around, and found continuity between the SPOUT harness and ground, which might explain code 212. I narrowed it down to the circuit between the SPOUT and PCM, where I'm seeing about 700-800 ohms to ground.

I disconnected the PCM, and the SPOUT harness immediately lost contact with ground. The wiring between the PCM and SPOUT seems intact, with less than an ohm of resistance between connectors.

So the SPOUT wire is not grounding out, but the PCM is granting the SPOUT a (resistive) path to ground. Is it supposed to do that, or did I just find an internal short in the PCM?
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Old 07-12-2018, 01:14 AM
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So, to update this thread, I got my hands on Ford's big ol' "Powertrain Control/Emissions Diagnosis" "On Board Diagnostics I" book. Unfortunately (or fortunately?) I lost all my stored codes when I removed the battery to clean up a tiny bit of corrosion that was starting on the terminals.

Started looking through the "stalls on idle" and "stalls on deceleration" charts, but since I hadn't driven it in a while, and had just put the battery back in, I decided to go for a drive and warm it up. Took a while for the symptom to return, but I finally caught it in the act and limped it back home.

Still had no codes, but it was running rough when I put it in the garage. So instead of pursuing codes or either of the stall charts, I followed the "runs roughly, at idle" flowchart. I eventually found a bad IAC valve, just like I originally suspected! It failed a resistance check, so I'm glad I didn't waste any time trying to clean it.

Got the new IAC valve in today, so I'll be back to driving it, and will report back if it tries to stall again, or if any of the codes return.
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Old 07-12-2018, 11:22 AM
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Damn. Hopefully its a simple thing like the IAC.
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Old 07-13-2018, 11:45 PM
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"....a bad IAC valve, just like I originally suspected! It failed a resistance check, so I'm glad I didn't waste any time trying to clean it.

Meaning the internal solenoid coil resistance was out of spec? Do you suppose the IAC fouling up idle quality might drive the PCM to throw codes in response to sensing incorrect idle responses, in error? imp
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Old 07-14-2018, 01:09 AM
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Yeah, no matter how much I wiggled my leads in hopes of a better connection, IAC solenoid resistance was bouncing all over the place. Mostly around the neighborhood of 170kΩ. I tested the new one before installing it, and it read a solid 11.1Ω (spec is 6.0-13.0).

I’ve already taken it through a couple of drive cycles, and so far so good. None of the codes have resurfaced. I know they're gone because I had to pull the battery, but I don't think I actually fixed whatever triggered those codes. I was hesitant to erase them because I’d heard that codes are supposed to erase themselves once a problem is resolved. Is that not actually the case, or does that rule only apply to certain systems (like OBDII, perhaps)?
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Old 07-14-2018, 08:32 PM
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Originally Posted by Urambo Tauro View Post
Yeah, no matter how much I wiggled my leads in hopes of a better connection, IAC solenoid resistance was bouncing all over the place. Mostly around the neighborhood of 170kΩ. I tested the new one before installing it, and it read a solid 11.1Ω (spec is 6.0-13.0).

Ive already taken it through a couple of drive cycles, and so far so good. None of the codes have resurfaced. I know they're gone because I had to pull the battery, but I don't think I actually fixed whatever triggered those codes. I was hesitant to erase them because Id heard that codes are supposed to erase themselves once a problem is resolved. Is that not actually the case, or does that rule only apply to certain systems (like OBDII, perhaps)?
There are several kinds of codes, according to my code reader manual, in EEC-IV, which became EEC-V in 1996 (OBD-II). One type is called a "Continuous Memory" code. I am not "up" on the differences, but am right now experiencing CEL turning on for 10 minutes or so, then turns off. 1994 GT 5.0 HO, Manual. The codes are misleading:

181 CM "Trucks Only) HO2S sensor fault unable to switch/lean during part throttle"

189 CM "Cars Only) Fuel system at rich adaptive limit at partial throttle/system lean

212 CM Loss of ignition diagnostic monitor signal/SPOUT circuit grounded.

The first two seem contradictory, though first is trucks only. If SPOUT circuit were grounded, would there not be any spark advance? I checked it, advances with jumper plug in place, 10 degrees initial shown no advance with plug removed.

The car runs just fine. Similar to your experience? imp
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Old 07-15-2018, 12:32 AM
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Yeah, same here. I checked the SPOUT wiring and couldn't find any evidence of it grounding out. I really don't know what could have triggered it. FWIW, I replaced both the coil and the distributor recently. I can't see how unplugging them could have set the 212 code, though. Maybe it was something else?

I'm trying to remember the last time I disconnected the battery, to help narrow down a timeframe when those codes might have been set. I guess it doesn't matter unless the codes return, but I'm just curious. They could have been stored there for a long time, seeing as the MIL never came on during driving. I only ever saw it when I'd first turn the key on, and recently when I went to pull codes.

At any rate, the car runs fine now and everything on it works, even the aircon. I have the initial timing (SPOUT disconnected) at 12BTDC, and it advances further when the SPOUT is reconnected.
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