I just replaced the Idle Air Control Valve and the check engine light comes back on and is giving the same code. The car currently idles at 950 RPM. Could it be that the IACV is bad? How do I know that the ECU is bad? My gas mileage is really bad. I went 250 miles and used almost a whole tank. How much is a new ECU any help is appreciated.

 

yup, likely the ECU is fried.

http://forums.maxima.org/5th-generat...l?ref=esp-link

i fixed mine by replacing the iacv and repairing the ECU.

 

^^^ yep... listen to this man.

 

Before you go buying another ECU, check your power steering air control valve - goes hand-in-hand with the IACV and resulting P0505 code. See diagnostic step #5 here: http://forums.maxima.org/5th-generat...is-thread.html

This will be especially revealing if there was no coolant on the stepper motor of your old IACV valve, and if the ohms test properly. Stealership was selling me on a new ICU but after thourough testing (and carefully following the steps given in the link above) I have determined that this valve is causing my problems.