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Check engine light has been intermittently flashing for a short while recently after acceleration. It's about due for plugs, but it's not throwing a misfire code. What's up with that? What's the threshold for throwing the code?

With a scan tool I did see a pending/developing code for a misfire on cylinder 1, but that never actually triggered the check engine light. It did start throwing a P0174 (bank 2).

I'll probably go ahead and change the plugs and check the coils since that's due, but I'm not sure that'll fix the P0174. Given that's one bank, I think I can rule out the MAF.

Oh, had a pending EVAP leak code, too at one point. Don't remember the actual code. That points to a vacuum leak somewhere? Possibly related to the lean condition?

I suppose the condition of the plugs will tell me if the engine has actually been running lean. If so, suggestions on what to check first? Intake manifold leak? If not, scope the O2 sensor?

There is a case of cat rattle, I've localized it to the second chamber on the driver's side, which isn't monitored by the O2 sensor. If that plugged something up could that be throwing off the first O2 sensor before the cat? Which bank is bank 2? Driver or passenger? Cat rattle is on driver's side.

AC compressor or the clutch is making a hideous growling / grinding when the compressor shuts off. I'll open a different question about that if it turns out not to be related - probably isn't.

Any and all wisdom appreciated. I'll go cruise the forums and eventually report back with what I found and what the actual problem turned out to be.

  • From cruising the forums, it seems like bank 2 is the side that doesn't have cylinder 1. I think on the 4.6L cylinder 1 is on the passenger side so that would make bank 2 the driver side....now I'm really wondering about that cat rattle... – Mark Johnson May 10 '17 at 19:36
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Changed the PCV valve since it seemed to be due on time and mileage even though it seemed to pass the rattle test. Also tossed a bottle of Techron in the tank. Cleared the codes. It's been thousands of miles and no problems. I'll update if it comes back, but for now, if you've got similar symptoms, you might try what I did since it's cheap and easy.

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