Have you cleaned the MAF wires?
Cleaned the throttle body?
Anyone played with the stop screw on the throttle body? This will upset the mixture a little.
What is the fuel pressure cold/hot engine?
The code you got is (probably a 543) means the engine stalled, so the system shut down - safety circuit.
If the fuel and ignition is up to par, I would scan it when cold to see what the temp. sender is telling the ECU the engine temperature is. Maybe it is running a warm engine cycle?
I think if you had a vacuum leak another code like lean bank 1 & 2 will pop up when the engine is warm.
