'00 Accent P1128

I have a 2000 Accent that is driving me crazy with code P1128.

Recent replacements:
1. O2 sensors
2. Flex exhaust pipes and gaskets. (flex part broke)
3. Plugs
4. Wires
5. MAF sensor
6. Just changed timing belt and all auxillary belts
7. PCV Valve

Car idles rough stopped at a light. I can feel the vibration in the seat. I have searched numerous times for a vacuum leak with no luck finding one.

Help...this code is driving me crazy.

I'M HAVING EXACTLY THE SAME PROBLEM! 90k TIMING BELT CHANGED AT 65k NEW FLEX NEW CAT NEW O2 SENSORS.GOT 66 MILES AND CHECK ENGINE ON AGAIN.HAD LOST 10 MPG WHEN FIRST LIGHT CAME ON.dDIDN'T GO FAR ENOUGH TO CHECK MPG (66MILES) BEFORE SECOND LIGHT.