ok, '04 6MT sedan, 92,000 miles.

I am getting slight hesitation/sluggishness when reving past 4k RPM. Also, gas mileage seems to be a little worse than usual.

Where to start? I'm not throwing any OBD2 codes, no CEL.

My first instinct is fuel filter and/or maybe a dying plug. Anyone else have any ideas before I start replacing stuff?

 

Just because you don't have a CEL doesn't mean necessarily that codes were not thrown. Have you checked? Reason I ask it that on my '03 6MT the knock sensor code (and few others possible) do not illuminate the CEL.

 

That's funny, I was just thinking the same thing. One of our work trucks had an o2 sensor go bad this week and it didn't throw a code. Going to check the G later this week.

 

Preliminary verdict: timing is max retarded - probably bad fuel.