I have a 2004 Chev Colorado with PO 141 & PO 506 code

If these codes only show after rain then the moisture is affecting the connections in the wires. Pull each connector apart and clean out with wd-40 or other water dispersant and ensure that the connections are water tight. Any dirt ,oil ,grease green gunk on the pins will cause a problem

Possible Bad COP Ignition Coils on #4 & #6 cylinder

Forget the 300 & 316 of no use to you

PO 304 is the same as PO354 or letter D
PO 306 is the same as PO356 or letter F

If the codes are the actual bad coils -you won't have to pull
the upper intake off

These codes are making me lean towards the ignition coil pack.My stepson's 2001 Sable 3.0 v6 had one cylinder misfiring(5-code P0305),which shares a coil with cylinder 1(code P0301).I diagnosed it by trading wire 1 and 5 at the coil,and the code changed to P0301.You have codes for the two cylinders on the same coil,so this is most likely it.(these codes would also trigger P0300(Multiple Misfires Detected) and P0316(Misfire Detected First 1000 Revs)).

PO305 Miss nr 5 cyl. PO316 Miss in first 1000 revelutions after start. Check Nr 5 cylinder plug, plug lead or coil over plug or nr 5 coil. Not sure what system that has. I suggest replace plug regardless but look at plug for track marks down side of plug & worn electrode etc... if all ok there check nr 5 injector.

code P0128 ECT ( electronic coolant temperature ) engine temperature to low ( replace thermostat ).

code P0300 engine miss fire detected ( replace spark plugs and spark plug wires )

code P0506 IAC ( idle air control ) system idle to low ( clean the IAC valve if problem persists replace the IAC valve )

Usually this problem occurs when a particular cylinder coil fails. You can swap coils of cyl 5 with another and see if the misfire follows to the cylinder that you exchanged coils with.If it does that confirms that that coil has failed. If it stays on the same cylinder you may have a spark plug or fuel injector issue.

there are four O2 sensors,you need to check the sensor on the drivers side exhaust,the front O2 before the converter

Yes they could a PO300 is a generic misfire code. PO301 would be cylinder number 1 so on and so forth. check the resistance of your plug wires they should be approx. 7000 ohms per foot. it could also be a coil over plug. primary resistance of the cops should be 1-3 ohms. but since this is a misfire it would be your secondary. which should be between 20000-30000 ohms. hope I helped you out. Happy Motoring!

google it. 2004 Chevrolet Colorado brake sensor or brake diagram.

po 305 is cylinder 5 misfire detected. I would check the plug wire for starters