My 2000 chevy venture idles rough, but if you give it a little gas it smooths out. engine light is on. i used a diagnostic machine. code said too lean bank one.

A scanner reading- P0171 system too lean bank 1 code is the MAF sensor.
The MAF sensor should be replaced. It is a fairly easy fix and relatively inexpensive. If you are running too lean on one bank, it is more than likely the MAF.
Let me know if this helps and if not I will try to help you farther.

An engine will throw this code if the O2 sensor in bank 1 finds a lean condition "too much oxygen in the exhaust" Two things you need to rule out - A faulty or dirty MAF "Mass Air flow sensor" you will find this on your intake. It will be a square box smack dab in the middle of all that tubing that leads up to your throttle body on the engine. Disconnect the cable and use the same pressurized air in a can that is used to clean home electronics. Check to see that there is nothing that is obstructing the cable to get a good seat.
- the second is there could be a vacuum leak. there is a vacuum line that comes off the intake usually going to the valve cover. Check to see that the tube is seated correctly and as far back on the nipple as possible. You would be amazed how much trouble a little vacuum leak will cause you.
- Now if these two are not the culperates behind your woes, then it could be either a bad O2 sensor (Usually around a 100 bucks at your local auto part store,unless you live in California and then you will enjoy paying twice that.) And last but not least it could very well be a bad MAF sensor,
Run through these steps and you should be able to knockout a few variables that will aid you in finding the source of your problem.
If you don't want to wait 50 ignition cycles to see if you remedied the issue you can go ahead and disconnect your battery and wait about ten minutes, what this does is reset the CPU in the car. If the fault is picked up again the car will let you know. Let me know if this helps, if not we have a few other things we can try.