[wolfox]

RPM should hold at about 650 or so when idle. The loud roaring/vacuum noise you hear may be just a fan clutch issue. Does the noise go away when you hold engine RPM at about 2500? Does it make this noise at startup, roar a little bit and then stop, only to roar again at take-off when you pull away from the stop? Does it eventually go away after a few start/stops or does it keep doing it? And what are your local temps like? It's been 98 degrees in the shade here, swampy hot too. When I have been running the truck more than 15 minutes with the A/C going full tilt, she roars at take off every time. The engine is just hotter than usual in these conditions and to bleed off that heat, the clutch engages and spins the fan up. When she cools enough, the fan slows and it's all back to normal. This would be normal behavior, what you describe; if it is really hot where you live right now and you have your A/C running.