If it is a positive fuel trim then the engine is trying to compensate for unmetered air. Did you remove any vacuum lines when you did the repair? If you did verify they are in the correct location and seated properly. An easy way to check for vacuum leaks is to take carb cleaner or starter fluid and spray different areas of the engine/intake/vacuum hoses and listen for an idle change. It works best once the engine warms up and the idle drops. Unfortunately if it is a vacuum leak that will affect the flow of air through the MAF sensor so a low MAF reading won't necessarily tell you the MAF is bad or not. You can also see if someone has a known good working MAF that you can borrow. I believe 96-98 use a different MAF sensor than 99-02.