Motor has noticibly different 'moods'

[CarbonZHP]

From day to day driving, in the same weather, the engine has been acting noticeably different. It feels almost as if the car is running on a lower performance map sometimes. The best indication of this is going about 50 mph, 5th gear, and flooring it. If the engine is in a 'good mood' the revs will jump up a little and pull smoothly, speeding up. If the engine is not running at its best, under the same conditions when flooring it the revs will jump up and then fall back down and make a struggling sound, with absolutely no torque, and not speed up at all. Car also seems quieter in this 'mood'. Vanos? Fuel pump?

[Johnmadd]

Possibly the clutch is going?

[CarbonZHP]

Possibly the clutch is going?

Auto

[johnrando]

I'd say mine has done that sometimes too, but no idea on yours. Maybe VANOS, but that should be consistent if it's an issue. Maybe somethings gunking up some stuff that could use some cleaning. Just guesses, I'm not much at diagnosing engine problems.

[CarbonZHP]

My only thought is that my fuel pump may be failing, and letting pressure out before I start the engine, maybe resulting in the ECU running a lower map.

[johnrando]

Hmmm. Could be. Miles? You clean MAF, etc?

[CarbonZHP]

MAF is clean. I have the oiled KN CAI so I do clean the MAF often. Miles are high, 124k.

[johnrando]

Fuel filter?

[CarbonZHP]

Not sure when this was last replaced. Have to check my records. Could have been as recent as 106k. If I stop the engine and restart 30mins later it will usually fix the issue. Cold start issue perhaps? I do park outside on a slanted driveway and leave at 7 every morning.

[Hermes]

Vacuum leaks