My colorado has 107,000 miles on it and never had a problem til my check engine light came on. Tested the codes and it said running lean bank 1. I replaced the first o2 sensor and light came back on. Now fuel cap shows on dash and stalls at least once a week for no reason.
truck stalls for no reason. on 2004 Chevrolet Colorado
Lean running conditions can be caused by fuel pressure of delivery issues (restricted fuel filter failing fuel pump), a vacuum leak usually at the intake manifold gasket, the air flow meter delivering an incorrect flow figure, or an incorrect O2 sensor reading can make the computer think the engine is running lean. A professional grade scan tool can read sensor information live rather than doing intrusive testing. Key scan tool information is also something called Fuel Trim figures, it shows how much furl the computer in your car is adding to make the car run (it shows the severity of the problem).
Your symptoms remind me of when I needed a carbon clean out. Got a "Lean Bank 1" code as well as low idle speed. Had it done about 50K miles...
I jsut had a simmilar problem with my 05 Colorado. The problem with mine was the fuel pressure regulator was leaking gas into the air box on top of the engine and causing it to do the same things. I would check this out as it wasnt a very expensive fix for me, around $50 dollars from Carquest. Its held on by two torx head bolts and the fuel rails should pull out after that.