Check engine light question??

What's the code ? P???

Maybe a dirty or malfunctioning MAF sensor could cause that. That might fool the ECU into thinking the throttle's almost closed. Just a guess.

BTW, an easier way to reset your CE light is to turn the ignition off and back on again 5 times while the truck is in motion and without disengaging the clutch in the process. It's easily done at any speed above 30 mph in the proper gear if you plan ahead so there's no other traffic to hinder while you're foolin' with your ignition. This works only if the problem which threw the code in the first place has been corrected.

If you go to AutoZone, why don't you use the Reset function of the Scan Tool? This is a far better way of resetting the Check light.

Lean can be caused by a vac hose that has come loose, or otherwise is the source of a leak.

Use the Reset function of the tool to be sure you have actually cleared out the codes, and write the codes down first, then write them down again when the light comes back on. Come here and tell us all of the codes that are on BOTH lists.

Maybe a dirty or malfunctioning MAF sensor could cause that. That might fool the ECU into thinking the throttle's almost closed. Just a guess.

BTW, an easier way to reset your CE light is to turn the ignition off and back on again 5 times while the truck is in motion and without disengaging the clutch in the process. It's easily done at any speed above 30 mph in the proper gear if you plan ahead so there's no other traffic to hinder while you're foolin' with your ignition. This works only if the problem which threw the code in the first place has been corrected.

A far easier way to reset the light is to use the Scan Tool. The OP is already going to Autozone to get his codes pulled (that sounds dirty when Bill Clinton does it), he should simply use the scan tool to reset the computer.

spray a shot of carb cleaner into the air intake across the MAF sensor and see if it goes out

Malfunctioning MAF (clean very carefully, it's an expensive filament) or vacuum leaks are quite common. So is plugged fuel filter/injector, or valve deposits, or a bad oxygen sensor. In other words, quite a few things that basically resulted in too much air and not enough fuel as seen by the oxygen sensor, assuming the sensor knows what it's talking about.

Please post the P-xxxx code. The fuel trims are probably pegged +20%. Some OBD-II scanners can tell you that, as well as oxygen sensor waveform.

I have had the same problem with my '99 Taco. Turned out to be the Oxygen sensor.

Doesn't a bad oxy sensor usually manifest itself with poor drivability? (rough idle, crappy mileage, reduced performance, etc.)

Normally, yes.

Or the sensor may be bad, not set any code, and be hurting the converter, setting the P0420 code (converter efficiency below threshold).

If it's the oxygen sensor, get the new Bosch planar type (not the old thimble) if possible.

Sounds like an O2 sensor. Next time it comes on, take a drive to Auto Zone. They'll put their computer on it and tell you what the problem is for free, or at least the one I went to did.