Using my SCT X4 to monitor a few things I'm noticing that my fuel trims at idle are lean. While driving around they hover right around "1.00" +/- .03. However when I come to a complete stop they nosedive to "0.80" , then go back up once I start driving. 1999 Explorer 4.0 SOHC, Car is running great. Is this normal? Thanks in advance.