Car runs perfect... comes to a light and rpm's pulsate from 500 to 1000 several times then stalls. No lack of power on highway or in town driving, plenty of fuel, no check engine light. I have scanned it, no codes present, problem started a few weeks ago drove it for 40 miles on highway then quit doing it.. now the more i drive it the worse its getting.. thought maybe fuel filter, but its clean, air leak... cant find one anywhere..maybe a sensor but that would trigger check engine light...... puzzled here