2003 Rav4 2.0 liter 2WD 161,000 miles. Engine hesitates when accelerating from a stop, and also when driving at about 40 mph when I let up on the gas, then try to resume acceleration. This began about 2000 miles ago and is slowly getting worse. Still very driveable, but left turns beginning to make me nervous. Motor starts fine, idles fine. No misfires, no smoke out the exhaust. No shuddering or unusual sounds. Check engine light has not come on and a scan revealed no codes. Please advise me of a possible cause - many thanks.