Nissan Repair: trouble codes, throttle position sensor, nissan sentra

Question
Hello,
I own a 1997 Nissan Sentra with 129000 miles on it. It has been a very good car. The check engine light came on and I went to a auto parts store and they pulled up code po446 Evap control system vent circuit malfunction and po505 idle control system malfunction. The car seems to run fine. What do they codes mean and is it seriuos?

Answer
The evap code is probably the gas cap being loose.  Make sure your gas cap is good and be sure to tighten it when you get gas or the light will come on.  If that is not it there is a charcoal cannister that has a vent valve that has gone bad.  Check the gas cap first.

The idle control system is probably the throttle position sensor or the idle air control valve.  I would go with the throttle position switch first as it is cheaper.  If you have a service manual you can look up the voltage values on both and check them before replacement.  Basically, the computer is saying the idle is out of range and it cannot bring it back to where it should be.  Make sure your car is tuned up before you start replacement of these parts.  If you have not done a tuneup in a long time that could be another cause so do this first reset the codes and drive it and see if the codes come back.