There was a girl here who had odd problems like this, she cleaned the MAF and fixed it. I don't remember the thread title, but some advice was given to her in that thread on how to clean. As I remember it, she cleaned it as she didn't want to wait for a new MAF, and her cleaning worked.

But I'lll never find the thread... One more thing, it is rare, but the CPS has caused trouble, the OTHER CPS: the CAM Position Sensor. Front of engine, on the left bank as you stand there looking at the engine.

Other than that, I got nothing. Have you checked the fuel pressure?