Exhaust in cabin

Feel lightheaded, nausea, headache & more. Sometimes strong exhaust smell, sometimes no odor. Fan on or off, closed recirc or not, heat or ac, defrost or any setting. Windows opened or closed. Uphill, downhill or straight stretch. In other words, no certain time.

had at dealer & 2 other shops, can't find problem. A few miles before I got to the dealer, warning light came on with lightening bolt. Dealer fixed via replacing map sensor, however this did not correct exhaust problem and they could not find a problem.