I have had the P1166 CEL for a while, and finally bought and installed the Primary (right after the exhaust manifold) O2 Sensor. Fixed that.

Then a P1491 came up regularly. I removed and cleaned the EGR with Thrust Starter Fuild,
Re-installed with the original gasket (it looked fine). Now, when I start the car it dies within 2 seconds.
I removed the positive battery terminal for 30-60 seconds, re-installed it and it seemed fine for 2 starts,
then back to stalling within 2 seconds after the start. If I give it a little gas for 2 seconds after the start, it runs perfectly. In fact, in economy mode, when the engine stops at a light, it starts perfectly when I remove
my foot from the brake pedal. The car seems to be running perfectly except for this anomaly.

NOTE: There are no CEL thrown - my ODBII tester comes up with "NO CODES".