CEL, intake noise....?

CEL came on in my truck tonite. 2010 DCSB Sport. Left & Right bank lean. I've been hearing a "whirring noise" coming from under the engine cover for about a month now (kinda sounds like an air leak on a big rig) but very subtle. I pulled the entire airbox off and looked at vacuum/intake lines, but all looks good. MAF cleaned, air filter clean, air to air connections checked aswell, but to no avail. My truck only has 62k on it. I swear it sounds like a possible crack in the intake manifold somewhere sucking in air but can't pin-point it....anyone have a similar issue ever??? I cleared the codes already with my scanner but they were P0171 & P0174 both at the same time, which leads me to faulty MAF or air intake leaks.

 

The first thing that comes to my mind is also a vacuum leak. Try isolating the brake booster by pinching or blocking the line.

I've also used small bursts of ether to pinpoint vacuum leaks while listening for a change in the idling engine, but keep all sources of ignition away and do it outside if you're daring enough to try it.

 

OK. I might try that. At first, I actually did think it was a bad check valve at the booster since the noise seems to be more noticeable from that side of the engine.