I would check the vac line to your fuel pressure regulator first.
The only thing the matter with deleting a rear 02 is that there is a Cat diagnostic test that can occur on 01+ if you delete your rear 02. Sometimes it doesn't matter whether it has an 02 emulator or the codes deleted. When it goes into this diagnostic, your fuel trims will rise and fall and the car may have a rough idle. The only way to fix this is to have someone with tiny tuner delete the test.
Also listen for the fuel pump to change pitch at key-on. You may want to test the voltage at the pump to see if the wiring is bad or what kind of volts you are seeing. I would just get a different fuel pump as well as a fuel pump rewire.
Easiest way to troubleshoot the Maf is to unplug it and see if the same thing occurs.
