good evening Gentlemen, I have a '02 Santa Fe V6 2.7l .Problem is this. Check eng light was on. Code PO174 and PO171 came up. Sprayed carb cleaner while running areound intake and vac hoses - no change in rpm. Car idles and responds well. no loss of power. Changed bith upstream )2 sensors and light came back on. Changed Mass Airflow Sensor and cold air filter. Car starts, idles up and down sometimes stalls. restart it will stay running and runs and responds fine. Now what? Light is off. I need to get the car inspected this month. What to do?

Go over this again, still some thing to check...P0174 HYUNDAI - System Too Lean Bank 2...Possible causes; Intake air leaks, Faulty front heated oxygen sensor, Ignition misfiring, Faulty fuel injectors, Exhaust gas leaks, Incorrect fuel pressure, Lack of fuel, Faulty Mass Air Flow (MAF) sensor, Incorrect Positive Crankcase Ventilation (PCV) hose connection...If the P0171 is combined with the P0174 code, it's very likely that the problem is caused by an intake leak. If there are no intake leaks, the next step is to replaced the air filter and clean the air flow meter. If the problem persist the front oxygen (O2) sensor may need to be replaced.

I changed both the left and right upstream 02 sensors and the Mass air flow sensor and air filter. light stayed off until this afternoon right after getting the car inspected. All was good. then light came back on with new codes. P1166 and P1167. Also when I started the car in the morning it raved up and down stalled out. I restarted it and it ran fine for the rest of the day..

From what I see you haven't done is change the oil, and have the EVAP system checked.... P1166 HYUNDAI - O2 Sensor System Lambda Controller at the Limit Bank 1....Possible causes; Air leakage or restriction in intake or exhaust system, Dirty engine oil or oil level too high, Front HO2S or MAFS contamination, Fuel system EVAP system Faulty sensor signals.......P1167 HYUNDAI - O2 Sensor System Lambda Controller at the Limit Bank 2....Possible causes; Air leakage or restriction in intake or exhaust system, Dirty engine oil or oil level too high, Front HO2S or MAFS contamination, Fuel system EVAP system, Faulty sensor signals...Meaning The Lambda closed-loop control system is included in the engine’ s control system. The control system regulates the lambda upstream with the HO2S signal. Rich mixtures generate high concentrations of CO, H2, and HC. Lean mixtures generate the high concentrations of NOx, and free oxygen. If the lambda controller reaches the maximum or minimum threshold, then feedback control is no longer possible and emissions will be increased. The ECM sets DTC P1167 if no proportional fuel adaptation occurs for a defined time after the lambda controller has reached its minimum or maximum threshold.