2008 V8 - 117,000 miles. Very well maintained.

Recently, I got the following codes, each within a couple weeks of each other:

P0420: Catalyst system efficiency below threshold (Bank 1)

Fine, one of my cats is going bad. Not real common, but whatever. A few weeks later I get:

P0172: Too rich Bank 1

OK, maybe this was the cause of the previous cat code? I do smell gasoline while the truck idles, but its not bad. But then, a couple weeks later I get...

P050B-84: Cold start ignition timing performance - Bus signal/message failure - signal is below allowable range

When this code pops up, I get a couple of weird issues. Sometimes my temp gauge just stops working and I can hear the engine fan really roar as I try to drive - there is def some power loss. If I shut the truck off and turn it back on, temp gauge is fine and everything seems normal again. I don't notice any performance issues otherwise.

Another oddity is when I turn the air on during idle, the RPM goes up and down between 300 and 700 or so. Turn off, it barely fluctuates.

So what do you guys think? MAF issue? Throttle body cleaning? Something else?

 

Sounds like a fuel injector for too rich, but I would try a fuel rail and intake cleaning first.

Its normal-ish for RPMs to fluctuate with AC on.

 

The "cat" fault can be just not being driven far enough to get the "cat" hot enough to clean itself or faulty heater on the rear O2 sensor on that bank. If you smell "gas" then you need to check for leaks in the fuel system unless you smell it from the rear

 

I had the same idle fluctuation with the A/C. I cleaned my MAF and TB, and it completely resolved it. The system rich code could be partly caused by the same issue, but a fuel rail cleaning may be needed as well.

 

Thanks to everyone that replied and apologies for the very late reply. I cleaned the MAF and TB and it resolved the issue.