The throttle position sensor (TPS) may fail. Common symptoms of a defective TPS can be rough idle, hard starting, hesitation on acceleration, poor fuel economy, and stalling.Google+
Car Problem Reports
Ford Crown Victoria Throttle Position Sensors May Fail and Cause Engine Performance Problems
Ford Crown Victoria Problem
Average Mileage: 143,500 mi (108,000 mi - 179,000 mi)
Visitor, 2006 Ford Crown Victoria, 179,000 mi
Low acceraltion bucking and jerking. Put it to the floor and it will snap your neck. Bad accelerator position sensor. Only on drive by wire cars 2005 and up. Parts places only show the part being on 2007 and up but they are wrong. Ford started using the drive by wire system in late 2005. We never thought to check it. Replaced everything but this part that supposed did exist on my 2006. Hope this helped someone.