99 explorer Lean Right, Left Bank code

My check engine light came on. I took to Auto Zone and they read computer code. Result: Lean Left Bank, Lean Right Bank. The salesman said it was probally O2 sensor. It has four; 1 before and 1 after on each bank. It also idles very rough until it is completely warmed up. This condidtion started long before the Check engine light came on. Are these conditions, the code results and rough idling, indicative of bad O2 sensors? What is curious to me is why both banks would indicate a problem simultanouesly with the occurence of the Check Engine light. I would have thought that the sensor would have gone out at different times.

From the sounds of it, you have a vacuum leak. Either a vacuum line has come off and that will be obvious from sound as you poke your head around the engine OR you have the notorious lower intake manifold gasket leak. I bet on the latter. It is definitely not the O2 sensors. Don't even think of replacing them, you'll need to save your money!

opera house is right on the money-- before the engine warms up and runs a steady idle try spraying carb cleaner onto the upper and lower manifods--and see what happens to the idle, they are, as operahouse said, notorious for manifold leaks. I just replaced mine it took about four hours- Haynes says to take off the valve covers-- not needed, gaskets from dealer were $20.00

a dirty maf(mass air sensor) will cause the same codes. spray the wire with an electronic cleaner

thank all of you very much for your input ... I will let you know what I find out.

a dirty maf(mass air sensor) will cause the same codes. spray the wire with an electronic cleaner
I had same code on my 98, cleaned maf worker for a short time ,just changed o2 sensors at 75000 a seams to have fixed it. Bres

I work for Bobby Likis Car Clinic in Pensacola Fla.I had 2 99 ford wind stars come in the same day with the same codes.Can't remember what #but i think it was 701,702.Anyway i found that it was the lower intake and the lower intake bolts that were causing the prob.i repaired the intake with the gaskets and bolts and also cleaned the chambers.This fixed the running errors.The ford dealer would not even touch either of these cars because they could not tell the customer what the error was, i banged my head for 2 days before i figured it out.Also if you take out the pcv valve with the grommet and look in the hole and see a small hole in the plate inside the valve cover you need to change the valve cover on the radiator side only.Oil gets through that small hole and works its way to the maf.Hope this info helps.Its a quick easy job.Dosn't look like it but it is.

reminds me of when i was in highschool i built a small block with short little aftermarket valve covers and used a long pcv valve it would suck up oil and smoke a lot. thanx i'm gonna look for that next time i see a ford with lean codes