P0112, P0171 and dies at idle: FIXED

[Keith1994SSEi]

The car is a 1994 Bonneville SSEi. New computer, new coil packs, new ignition module, recent plugs and wires, new fuel filter, new radiator. Car runs down the road good.
The codes above seem to be permanent--they won't clear. I have EFILive V4 which is a scantool using my laptop and a special cable. Anyway, P0112 is "Intake air temperature circuit, low input." On the computer it shows MAT (manifold air temperature) at -50(f), which is pretty low considering that it's 87 degrees (f) outside. So what sensor sends the intake air temp to the computer? Doesn't seem that it would cause it to die...
P0171 is "System too lean (bank 1)." I thought this might be the O2 sensor (in spite of the fact that there were not other O2 sensor-related codes), so I replaced the O2 sensor. It didn't help or clear the code. In any case, this shouldn't cause it to die either. What other possible causes of this code are there?
I can clear the codes, but they pop right back up.
Car dies when idling. This doesn't happen very often and usually only with extended idle time (2+ minutes). Immediately after it dies, there is NO power to the accessories (power windows, locks, sunroof, radio) and it WILL crank but WON'T start.
The idle speed (when idling successfully) is in the high 600 rpm range in drive, in the 800s in neutral. Smooth idle until it stumbles and dies. So, good idle speed, it just won't keep it up for a long period.
Car runs great going down the road. Excellent power--it will spin the tires on hard acceleration (with traction control off), and accelerates smoothly at low, medium and wide-open throttle, so I doubt it has a fuel problem--plus I just recently replaced the fuel filter.
All vacuum hoses look good. I haven't done the WD-40 test yet, but good idle and smooth running--when it's not gasping its last breath--seem to indicate there are no vacuum leaks.
Could this be an emissions system issue? I'm stumped.
Keith

[harofreak00]

Welcome!

The P0112 Intake air temperature circuit, low input, is probably your IAT (intake air temp sensor) which is located on the airbox. That shouldn't be a huge problem and shouldn't be related to your stalling.

What did the o2 sensor look like when you pulled it? What did you replace it with?

I'm not exactly sure where you point you with the stalling, as you say it idles fine for 2 minutes before acting up. When it doesn't start after it dies, how long does it usually take to start? Have you confirmed that you are getting spark and fuel at that point?

You got a good start, not many people figure out how to connect their 94-95 OBD1.5 cars before finding this site. We should be able to help you.

[Keith1994SSEi]

Thanks for the quick response.
Anyway, the O2 sensor was pinkish when I pulled it. I doubt that it was bad, as replacing it didn't clear the code. I replaced it with a Delphi O2 sensor. I never use Bosch. I learned that lesson long ago. I never heard of Delphi before but they are apparently an AC-Delco factory replacement... I like Denso, but didn't want to wait 2 days to get one in the mail.
As for re-starting after a stall, sometimes it starts right away, sometimes you have to wait up to about 5 minutes. The odd thing is the loss of electrical power to the windows, door locks etc. I'm thinking it might be a bad ignition switch (not the key cylinder but the actual switch buried under the dash somewhere). The starting circuit would appear to be OK, since the engine cranks, but the running circuit, as it were, is apparently not making good contact at some point, like when it's warmed up and the alternator output is lowest (at idle) and insufficient juice gets to the injectors, spark plugs and fuel pump. So the engine dies. When you first try to start it, the starter will spin; but if insufficient electricity, or no electricity, is going to the injectors, pump and/or plugs, no spark, no fuel, nothing but cranking. It's a theory anyway.
What do you think?
Keith
1994 Bonneville SSEi

[Mechanical Mike]

Excellent theory, its actually a fairly common problem on the pre-2000 Bonnevilles. The fuel pump, power windows & locks share a common ground that can corrode. This ground bus is located near the driver's door sill. I'll add some pictures that show the location. Pull the metal bar from the bus & clean both the male & female terminals. Apply some dielectric grease & reassemble.

Did you find the intake air temperature sensor?

The P0171 code is usually caused by a vacuum leak or a fuel delivery problem. If cleaning the bus doesn't get rid of the code then scan for LTFT (long term fuel trim), STFT (short term fuel trim) & MAF sensor frequency. Get all three readings at idle & again at around 2000 - 2500 rpm.

[Archon]

IIRC, when BillBoost37 chased that problem around (P0171), he finally found the resolution by replacing his battery cables, and cleaning up the ground at the ICM.

[Keith1994SSEi]

This is good stuff! I'll chase that ground first, because this car sat in a field for over a year and almost literally filled up with water from a leaky taillight lens, (which allowed water to fill up the trunk and overflow into the interior!) and leaky doors (which contributed to the interior flooding). I fixed the leaks, but am still running down problems resulting from them. In fact I've had trouble with that ground before. Bottom line is that the grounding bar and its connection might be corroded beyond repair. That's easier (and cheaper) to fix than a new ignition switch.
I did find the IAT sensor although I haven't replaced it yet. It seems to be the least of my problems...
On the other hand, this car has gone from being a non-starting flooded junker to a tire-spinning smooth running machine with cold air and excellent handling (for a front wheel drive machine anyway). If I can get rid of the stalling I might even let my wife drive it. Of course that will make my teenagers unhappy. ;-( Too bad.
Keith
1994 Bonneville SSEi
1995 Cadillac SLS
1995 Ford 150
2002 Suburban
1995 Cannondale R400 (really good fuel efficiency)

[lash]

Kepp us informed as to your progress. Each problem child can be a learning experience for us all.

On another note, be warned that once you let your wife drive it, you may not get it back.

[Mechanical Mike]

In fact I've had trouble with that ground before. Bottom line is that the grounding bar and its connection might be corroded beyond repair.

You can just cut the bus out & solder the wires together. I'd use some brush on wire insulation to keep any water out.

[Keith1994SSEi]

I cut all the wires and soldered them together. It hasn't died since. RESOLVED. Thanks to all that helped. I'll keep in mind the other suggestions in case we get a recurrence.
Keith