both obd codes po446 and po506 are coming up on 2005 Chevrolet Colorado

idels rough but run good, or so it seems

Asked by for the 2005 Chevrolet Colorado
Which motor? 2.8L or 3.5L It matters for diag. P0446 is an EVAP system code, and P0506 has to do with the Throttle Actuator Control (electric gas pedal) system.
The 3.5L
For the P0446 code, that is the EVAP Vent Solenoid performance code. Most likely you need to replace the Vent Solenoid. We do a lot of these. But, before wasting money or throwing parts at it, I would reccommend inspecting the EVAP lines and hoses for any leaks to be sure. Also remove and inspect the Vent Solenoid for dirt or mud being in it, and check the wires and connector to it. The Vent Solenoid is located underneath the rear of the vehicle on a frame crossmember behind and to the left of the muffler. It should be mounted with the Charcoal Cannister. The P0506 code is for a low idle condition, which may explain the rough idle. Does the vehicle die if you turn the A/C on? Just curious. I just had a vehicle with this condition on this motor and wound up having to replace the Throttle Body Assembly. Remove the TB Assembly and try cleaning it thoroughly. Also check for vacuum leaks and replace the PCV valve. If the code and idle problem are still present or come back after these repairs, you will need a scanner (not code reader) with actuator output functionality to test whether the PCM is commanding the correct idle and whether or not it is getting the correct feedback information from the Throttle Position Sensor on the throttle body. Testing the sytem with a scanner will ensure you find the correct problem. However, if the code and idle problem return and you don't have access to a scanner (and don't want to pay a shop for diag) you can just replace the Throttle Body assembly and hope that it is the problem and not the PCM or wiring. that will be a costly guess though. If you have access to diagnostic equipment and want to email me your email, I will gladly send you the wiring schematics and diag charts. My email is
Thank you very much. I've already located the Vent Solenoid and will
clean it up in the morning. We live down a very muddy road.
The truck runs good even with the ac on. Just idles terrible.