Blazer 2001 4WD 4.3L. In trying to track down the cause of my lean codes P0171, P0174 I smoked my intake manifold through the brake booster line. I left all connected except the MAF and plugged the rubber boot that goes to the back of the MAF. The majority of the smoke I saw was coming out from what appears to be the timing chain cover. I confirmed this with some soapy water. With or without the breather tube and PVC hole plugged this happens. Any idea if this should happen? Could this be a sign of a leaking intake manifold gasket inside the engine rather than external? If I pull the oil dipstick I will get smoke there as well. I had a little bit of smoke came out the throttle body shaft and some from around where hood seals to the throttle body otherwise. Before I go an do an intake manifold gasket I want to be sure this should not occur. I have no issue with loss of coolant, and can not find and external intake manifold leaks via smoke or carb cleaner.