enerkachoo

I'm driving a 2004 heritage, 4.6L triton. I went for a long stretch down the freeway, got off at my exit, and at the first red light I noticed a very rough idle: Truck shaking, tach bouncing between 500-1000 (stalled a couple times, started back up). I decided to keep driving, and above 1500 RPM the truck worked just fine. Took it to the nearest parts shop, scanned it, and got codes saying I'm running lean. I drove it back home an hour away down the freeway, and drove to work the next day. The only problems I have are in idle, not at speed. What could it be?