I have a 2000 Oldsmobile Alero 3400 that runs rough at idle, surges and would eventually stall. codes p0131 and p0171 for lean condition, replaced the upstream o2 sensor was fine for week, and returned with surges at idle, on the highway and off idle the engine runs fine, replaced the maf sensor, cleaned the iac vlalve, inspected the map sensor vacuum hose, removed the egr valve and plugged the egr port, no change in idle, when the maf sensor is unplugged the idle levels out, smoke tested the engine and cannot see any leaks other than the base of the egr valve and a slight smoke around the shaft of the throttle body, any info would be great.. Thank you Ernest