My 2006 Tahoe, 5.3l has just developed exhaust smell in the cab, especially while idling. If i use the recirculating feature of the A/C it doesn't smell nearly at all. But with regular outside vent air I get exhaust smell inside the cab pretty bad. I have looked over the exhaust system and found no cracks, splits or leaks. No hissing noises anywhere. I leaked checked the manifolds and pipe connections to see if there wasa problem but nothing. Is there something up font, maybe to do with the smog system that could be filling the engine compartment or cab with exhaust smell? Thsi is not rotten eggs smell so not catalytic converters either. Need some help as my wife is very susceptible to exhaust smell, makes her very sick. Thanks!