My 99' xc70 is running rough. I changed the spark plugs,fresh gas...when I reach about 3.5 RPM'S the check engine light comes on/off.....sensors in the gas tank? Bad coil pack(s)????????????It has 131,000 miles on it.The Volvo dealership said I didn't have to worry about the sensors in the gas tank...just drive it....it would be about $900.00 to drop the gas tank and replace the sensors. HELP PLEASE!!!!! THANK YOU!!!!