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Discussion Starter #1
My truck has been running code 44 for about a month now. At first, it was just the light. A couple days later, the idle became rough, and I replaced the O2 sensor. This fixed the issue for about 200 miles until the code and the rough idle returned. I replaced the O2 sensor again under warranty, and it worked fine for another week or so. During this time, I replaced the fuel pump when replacing the sending unit to upgrade to a 20 gallon tank, so I do not believe the fuel pump to be the issue. About a week after replacing the O2 under warranty, the code came back. It has been about 2 weeks since the code came back. It does not idle rough, but it does occasionally stumble at a specific RPM while accelerating. When the code came back, I replaced the O2 sensor with an AC Delco unit, thinking that the Bosch sensors were just hitting the fan. The AC Delco sensor made no difference. I replaced the fuel filter (about 30,000 miles on the old one) and ran some fuel injector cleaner through the tank, but those have made no difference. My book says to test the MAP sensor by unplugging the connector, and that the ECM will substitute default values for it. If the MAP sensor is bad, the lean condition should go away after unplugging the sensor. After unplugging my sensor, it ran worse, and stalled out when I tried to drive. At this point, I'm torn between replacing the exhaust manifold, or tearing the TBI apart and replacing the injector and pressure regulator.
 

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Discussion Starter #2
I noticed that fuel was collecting on top of the intake manifold behind the TBI, so I pulled it off and rebuilt it. No more fuel on the manifold, but I'm still experiencing the same symptoms.
 

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Check over your O2 sensor wiring. It seems everytime you play with it, it works for a while. Could have a bad connector or burned or chaffed wire(s).
 

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Discussion Starter #4
It's been a while since this issue popped up and I've been fighting it on and off, mainly throwing parts at it. A brief summary of what's going on as of present: Once warm, the truck idles high at stoplights for several seconds before the idle comes down. Occasionally, idle is low to the point where it almost struggles to continue idling. Also occasionally, while accelerating, the truck will start to stumble, as if not getting enough fuel. I can power through or reduce throttle to fix it, but maintaining that throttle position sounds like two step. I can smell it running lean. It throws code 44 and has recently started throwing code 35.

And here is a list of parts I've thrown at it:
  • 2 or 3 O2 sensors
  • Fuel pump (mainly an excuse to upgrade to the 20 gallon fuel tank)
  • Fuel filter
  • Rebuilt TBI
  • New exhaust manifold
  • Throttle position sensor
  • IACV (after code 35 was thrown)
  • MAP sensor
  • Checked for vacuum leaks
I checked for vacuum leaks around the usual suspects - EGR valve, vacuum lines, TBI gasket, and the intake where it meets the head, and found nada. I'm not quite sure what I'm missing here, and at this point I'm only a few parts away from a brand new truck.
 

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Discussion Starter #5
A promising update for anyone who may be following along.

I found a brand new AC Delco EGR valve still in the box lying in a pile of other S10 parts I had. I figured it wouldn't hurt to install it. I pulled the old one off, and YUCK! I believe it's 3 years old, but it was caked in carbon. I'm not sure what brand the old EGR was, probably either from AutoZone or Advance - definitely not AC Delco. You couldn't reach under to feel the diaphragm like you can with an AC Delco, and I don't have a vacuum pump, so I had no way to test it.

When I went on a test drive, it was somehow worse. Idle was all over the place - first stupid high, then struggling to idle at all. When accelerating, the stumbling was much worse, almost to the point where I couldn't accelerate at all. I could even feel a slight stumble when cruising.

I got back to my apartment to read codes and, in addition to 35 (IACV) and 44 (lean), it also threw 24 - vehicle speed sensor.... on a truck with a cable speedometer? I unplugged both battery cables, and touched them together to clear anything in the computer. I took the same route as the first test drive, and after the computer relearned what it needed to, it ran good at idle, cruise, and under load. Hopefully, this saga is over.

Lesson (one that I've ran into many times, but have yet to actually learn: Engine codes don't tell you why your car is sick, they tell you what the symptoms of the sickness are. Instead of triyng to fix the symptoms, fix the sickness.
 
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