Originally Posted by Kingtal0n

Here are some possibilities for you to consider:

1. the wideband is wrong. MAYBE. Consider for a minute- if it IS wrong, then your engine may have NO PROBLEMS currently and where located.

2. The wideband is right, and something else is wrong. WHAT ELSE?
there are many possible causes for this situation, such as exhaust leak / improper sensor [location/environment]

So I feel the proper course here is to verify the wideband FIRST. Dont do ANYTHING dont touch ANYTHING do not exchange ANYTHING before you make sure the wideband is reading right.

here is how I would start (from the cheapest quickest solution as always do the cheapest, easy most simple things first)

Buy a narrowband sensor. Ensure there are no exhaust leaks. Put your hand everywhere when the engine is cold feeling for puffs of air-
Run the narrowband sensor and see what the wideband says. If the narrowband is working, and the ECU is completely OEM, you should be seeing it swing around 14.7:1 air fuel ratio, during the times while yours is reading 16.5 right NOW.

Here are the possibilities, and the solutions for each now (the next step)
a. You install a new narrowband and the wideband reads 14.7 at idle/cruise. Everything is fixed.
b. You install a new narrowband and the wideband STILL reads in the 16's. Proceed with:

Install ANOTHER wideband sensor. This is weighed against the probability you have access to one. The AEM requires or advertises that "no calibration is necessary" for their units. You need to verify that the AEM is reading BAD, because the only other explanation for what you are seeing is an issue with actual fueling. Which means your engines life is in mortal danger. Please understand that if that wideband is RIGHT and doing its job you may need to fix an actual fuel problem which can extend from the tips of the fuel injectors to the ECU itself, all of which is MORE costly and time consuming that just swapping a wideband to verify the issue is actually fuel related.