...unless I can fix the Mustang within the next couple of days.
The ’95 GT (stock 302) in my avatar has been pretty reliable, for the most part. I hardly ever see the check engine lamp, except for when I first turn the key forward (lamp check). Oh, and today when I went looking for stored codes and counted the flashes.
Why was I looking for codes? Well, on my way home today, my car developed a nasty tendency to stall when I would slow 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. It 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
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
Now I could try chasing these down one-at-a-time, but I’m scratching my head over whether they might have something in common? I’ve got Ford’s regular Service Manual, and the EVTM, but unfortunately not the “Powertrain Control/Emissions Diagnosis” volume. As near as I can tell, the only thing that the IAT, ECT, MAF, SPOUT, and IDM all have in common seems to be the PCM. As you can imagine, that’s a conclusion that I’m hesitant to jump to...
All major ground points are clean and tight. I’m reading less than 1 ohm between the battery, engine, chassis, & PCM grounds. Battery passed a recent load test and its voltage is currently 12.5V. With the engine running, the charging system brings it up to 14.2V. And I put a trickle charger on the battery to help make up for all the extra cranking that the starter had to do today.
I tested the ECT sensor about a week ago (good), but I don’t have testing procedures for the other sensors. FWIW, all sensors appear to be intact, and the wiring looks good too (as far as I can see them before they disappear into the harness, that is).