The tests were performed to determine the effectiveness of the State's mandatory inspection and maintenance program. The effectiveness was to be determined by measuring the exhaust emissions of over 600 vehicles after inspection and maintenance and thereafter quarterly for a one-year period. Not all of the vehicles completed the full sequence of quarterly retests and therefore, as a continuation of that effort, this test group was established. Fifty quarterly retests were performed on twenty-two vehicles. Each retest included an Idle Test, FTP, and HFET at the HTS facility. A diagnostic check was performed on each vehicle prior to being preconditioned for the FTP. Thirty four vehicles with suspected EGR System malperformance were recruited for Test Group No. 5.