1999 Yukon rough idle

[tonye456]

Hey everyone. Well I'm working on a 1999 Yukon with a 5.7 V8. The truck runs great on the city and highway but runs rough at idle and takes a few cranks to start the engine... OBD Codes are P0300 Random Misfire, P0172 System too rich bank 1.
So far we have replaced the spark plugs, ignition coil, cleaned out the throttle body and MAF sensor, ran a few bottles of injector cleaner and checked all the hoses but we can't seem to find the culprit... Anyone have any experience with this issue? I was thinking of checking the O2 sensors as I did get a P0134 O2 Sensor Circuit No Activity Detected but after a code reset we have not been able to get the code to come back Thanks.

[StumpedGMowner1]

Have you replaced plug wires?

[StumpedGMowner1]

This wont be vacuum leak related at all. So you can rule that out. Even a leaking intake gasket will throw lean codes not rich. Without viewing any live data off the pcm all i can do is give you ideas. Distributor cap and rotor worn, plug wires worn and leaking, bad fuel pressure regulator in spider leaking fuel into vacuum line, stuck open or partially clogged injector. O2S11 can cause this but in my experience its almost never the culprit. I would start with finishing the tune up with new wires and cap n rotor since you already started the tune up anyway and your getting an accompanying misfire code.