On April 2, 1995, approximately 1930 mountain daylight time, a Mooney M20J, N4478H, was substantially damaged when it collided with an automobile during a forced landing near Tijeras, New Mexico. The commercial pilot and automobile occupant were not injured. Visual meteorological conditions prevailed. The following is based on the pilot/operator report. The airplane had been flying at 12,000 feet MSL (above mean sea level) in instrument meteorological conditions with occasional light rain. As the airplane emerged into visual meteorological conditions, the pilot noticed the cylinder head and exhaust gas temperature gauges had "dropped off the scale." He adjusted the mixture and the instrument readings began to return to normal. Shortly thereafter, the engine began to run rough and lost power. The pilot's efforts to restore engine power were unsuccessful. He declared an emergency with Albuquerque Approach Control, then made a forced landing in mountainous terrain on New Mexico Highway 337. During the landing roll, the left wing tip struck a parked car. After relating these events to a Federal Aviation Administration (FAA) inspector, the pilot said he did not remember if he had switched fuel tanks in his attempt to restore engine power. The fuel selector was found positioned on the left fuel tank. At the request of the pilot, the airplane was transported to Clearlake, California, for repairs. In the presence of an FAA airworthiness inspector, the engine was functionally tested on August 23, 1995. During the first test, the engine ran rough at high power settings (2,650 RPM and 26 to 28 inches of manifold pressure), and the fuel pressure fluctuated between 5 an 14 pounds per square inch (psi). During the second test, engine power again ran rough at a high power setting (2,600 RPM, 25 inches manifold pressure). Fuel pressure was 3 psi. When the fuel boost pump was turned on, fuel pressure rose to 5 psi. The right fuel tank was selected and the engine ran smoothly. When the fuel selector was switched back to the left tank, the engine ran rough. The left fuel tank finger screen was removed and found to be plugged with what was described as "leaf roller bug." After the finger screen was cleaned and reinstalled, the engine was tested again and operated smoothly at all power settings on both the left and right fuel tanks.