I happen to have the lower engine encapsulation panel removed right now, as I fixed an oil leak recently (new oil pan gasket) and wanted to easily inspect after driving a few hundred miles to make sure it was stopped. Doesn't seem to matter if the panel is on or off, though, as far as power is concerned. I'll be re-installing the panel as soon as my tranny cooler line arrives and I replace that, along with changing the ATF to Mobil-1.

About the airbox, here's an interesting item I just picked up, it's an airbox shielded with space-age insulating material:

http://500ecstasy.com/forums/showthread.php?t=814

My IR thermometer showed the stock airbox top surface was in the 150F range with the engine warm! Yipes. And that was with ~80F ambients. I'm curious how much heat the insulation/foil will reject. That only reduces intake air temp, but I'll take anything at this point.

About the low-end power. My OM603 turbo diesel seems to be snappier down low, say 2000-2500rpm, and it shouldn't be - the M119 is rated at lots more torque, even off idle. That's why I'm suspecting the camshaft advancers aren't advancing, they advance in the low RPM range to boost power, then retard at high RPM (retard is the default/normal position for starting and idle as well). The cam timing data is in the intro manual, IIRC, I just looked at it a couple weeks ago - I'll find it again and post the numbers here, as someone else questioned this earlier.

Problem is, I have ZERO idea how to measure cam advancement (or lack thereof!) with the engine running. If the solenoids just get a plain 12VDC signal, I guess I could connect a bulb in parallel and run it into the interior and go for a drive, and see if it lights up at the RPM range specified in the manual? That wouldn't prove the solenoid(s) were working internally, but would eliminate the computer & electronics as an issue (for cam timing anyway).