Random occurrence twice back in June, within a couple days of each other, both times the code set at the point of an aggressive acceleration from 60-65 mph near the end of a 2 hr highway run.

Cleared with no further recurrence. Performed a number of maintenance items not necessarily in response, but these are potentially pertinent:
Renewed engine air filter
Renewed engine fuel filter
Removed/Replaced upper intake manifold to facilitate cam-cover gasket renewal
Renewed spark plugs
Renewed bank 1 coils
Moved coils previously installed in bank 1 over to bank 2 to facilitate installation of new ones on bank 1.

All the above accomplished at the same time; no running in-between. After reassembly, I ran the "Monitoring Conditions" listed in the DTC 3 or 4 times with neither the code set nor pending. (Was also fitting some new suspension gubbings so had ample opportunity to idle for 10 minutes but not drive)

Back on the road, and for about a week, I had "P0174 Pending" which I surmise means it occurred but on less than 2 consecutive trips. Finally, on the evening commute last night, I got a "for Real" P0174 with associated "Restricted Performance." However, I happened to be collecting data via ScanTool OBDLinkLX adapter and TorquePro app. The code set somewhere in the region described by jpg's "2016-09-17....-1" and "2016-09-17....-2"
For giggles, I've attached a pic of the fuel trims at idle about a half hour later upon arrival at home.

I have ordered a can of BG44K but it won't be here until Thursday. Considering maybe trying a snootful of Chevron Techron fuel sys cleaner this weekend as it's likely locally available. Trying to prep this one for trade next weekend for my daughter's 03 which has been too long in the field sans-service in the wasteland known as Louisiana. So I'd much rather sort this now and have a weeks' worth of 100 mi. daily commutes with no problems than be still sorting it when it is time to make the 6-hour trek to Monroe, LA.

All ideas welcomed.....well, except inquiries about freeze-frame data (John!)

Maybe TorquePro, but I've asked it for freeze-frame on multiple cars with multiple BT Adapters and it always spends a few minutes "Gathering data" and finally returns more than a screenful of parameters but each and EVERY time, their values are nothing more than a mixture of "0's" and "-40C's" I find this useless and don't download it for further analysis.

 

Sent it to Fort Worth with the girls today, (nearly an hour of mostly highway each way, plus considerable stop-n-go as they spent the day shopping) then a run to Bridgeport and back, about 5 mi, each way, 60-70 mph.

WHen she was all done with it, I checked codes (only P1000) grabbed a freeze-frame so you can see what I'm talking about above, and then ran it up to 2500 rpm for a bit, and have included the data file from idle-2500-idle.

Edit: Added a shot of the FT's at Idle/2500. Looks like bank 2 is adding more fuel wrt bank 1 at elevated rpm's no-load. I've got to ponder my navel or play fetch with the dog and reason out what that means......

 

Both short trims jump from -20 to +20 or so. You probably have bad MAF.
Remove it and clean with cheapest brake cleaner.
+ 15 short trim at high RPM can be dropping fuel pressure, bad fuel pump/regulator. Fuel pressure should be on scanner.

 

Both sides trims are very similar so you're looking at something common to both banks.

They don't drop from biggish +ve (at idle) to near 0 (at 2500) so not a typical air leak. (Likely not an air leak at all, unless you've 2 faults.)

Bad MAF (dirty/etc) or fuel pressure - yep good thinking.

I don't know if bad coils could do it (causing misfires, which of course are and look like excess air, thus reported (wrongly but hey) as lean) but with what's been done so far I'd be going with the existing suggestions.

In case you have (or have recently had) the battery off, it clears the learned trims etc. Then it has to relearn and it does that via the STFTs. They migrate into the LTFTs (the names are a clue) so to see what the LTFTs are you need a while to give it a chance to figure them out.

 

Numerous Fuel Pressure columns in the data from the scanner, all bereft of data, however.
Fuel pressure(psi)
Fuel Rail Pressure(psi)
Fuel Rail Pressure (relative to manifold vacuum)(psi)

I've got another MAF, may fit it up if I locate it. Obtained in a vain attempt to rid the same car of recurrent P0101 in former times.

 

Pah. It ought to be able to read at least the standard fuel pressure!

(At least mode 1, PID 0A - that's hex i.e. ten in decimal. I think PIDs 22 & 23 are standard, too, not so sure about 59)

https://en.wikipedia.org/wiki/OBD-II_PIDs

 

The car was well-behaved this weekend and for the morning commute this morning. I got a "pending" P0174 this evening on the way home about 30 minutes or so after P1111 set indicating all emissions monitors were good. I've fished out the spare MAF and fitted it tonight. Haven't had a chance to download and process this evening's data, but below are a couple of shots of this morning's commute: one at about 2300 rpm steady-state and another at idle after about an hour's operation. I managed to get fuel pressure data this time,(Pretty much steady on 55 psi) and scaled it up so it could display with the other data, likewise the MAF data. LTFT's look a bit high when off-idle.

I've persuaded myself it is not a vacuum leak or I reckon it (the code) would show up on the 10 min idle monitor test in the DTC guide.

 

Those are so cluttered - a triumph of too many things crammed on each. I think they may show -ve trims so running rich at idle?

But +ve at 2300?

If so something other than an air leak, maybe bad MAF?

 

First of all, the throttle position line in the post #7 pics is bogus - I found an error this morning in that I was performing a calculation on the wrong column.

The 2300 data is taken from a section of the drive where cruise-control is active, 75 mph, and although predominantly level, there is the occasional rise and fall of terrain, as well as slight variation in temperature. The idle data is taken from being parked at work with the xmsn in P and the park brake set.

The replacement MAF I fitted last night seems to have calmed things down a bit. I did not clear the "Pending" P0174, and drove it to work this morning, then out to Autobahn Jaguar for parts and back at lunch; still no P0174, so still hasn't occurred on 2 consecutive OBD "trips."

Here is a snapshot of this morning's run: (sampling is taken at 1-second intervals)
Granted, busy charts, but there were questions about the MAF, and the fuel pressure....then I pulled in throttle position to see if it explained movements in the MAF data that looked otherwise unrelated to the other data.

 

Graham, Norri, Don, et al...I'm calling this one sorted by virtue of reverting to a previously-used MAF if you want to add "solved" to the title.

I replaced the MAF some time ago due to recurrent P0101 codes. I've since determined that was caused by a clogged intake air filter. Refit the previous MAF the other night, didn't clear the pending P0174 and it was gone after 3 or 4 trips and hasn't returned. Also, the data in post #9 is post-MAF change and reflects a much tamer picture.
Having said that, I did dump two cans of Techron Fuel System Cleaner (Sufficient for 24 gal) prior to topping up last Sunday morning, and topped up today (14.3 gal of 18.4 total capacity) after adding 11 oz of BG44K (sufficient to treat 20 gal, per instructions) so I can't say without doubt that it was the MAF, though the data cleaned up markedly immediately after MAF change, and only several days into the fuel treatment.