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Just updating to basically log my situation and will update for the benefit of future google keyword searches later.
Sitrep. Checked the air box and filter thoroughly. All clean. Checked the hose from maf to throttle body. Also clean. Seems therefore engine should be getting all the air it demands.
Car is in the shop getting the bank 2 variocam mechanism changed. More testing with the Duratech showed this playing up repeatedly but no issues with bank 1. Given the part cost and the minimal labor savings, I am only getting bank 2 changed.
The technician noted some smoke on starting. I had previously checked the crankcase vacuum for pressure to see if changing the AOC was required. The vacuum was not excessive, but the tech suggested changing it anyway given his experience with that amount of starting smoke.
Will also get a fuel flow performance check when it is on the lift and to save spraying gas over my garage floor. That should rule out a failing fuel pump or blocked filter.
I will report back. In theory, any one of these three things could cause a lack of power. Fuel seems the most physical explanation. Unless I misunderstand the system, the AOC failing could cause a vacuum leak and so a loss of power, but given the modest crankcase vacuum and fairly small fuel trim values noted by the engine, this seems unlikely to me, although I am a novice.
The variocam should only cause a lack of power from 2000-5500rpm on one bank if affecting things, but reading the technical articles about how it works, above 5500rpm the cam pops back to the zero idle position. Since I measured the wheel power from 1500-7000 rpm the power should be nominal above 5500rpm irrespective of the variocam oil seal leakage rate. I saw no signs of sticking at any intermediate value. It wanted to get to zero.
Philip
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