I'm starting a new thread.. remaining issue(s) have nothing to do with engine/chassis vibration. Excessive vibration has been 100% solved. In essence it was running lean at idle with poor atomization and a weak spark.

To save newbies the headache of sorting through this very long thread that got off topic (my fault, sorry). If you're experiencing excessive engine feedback/vibration through the steering wheel/chassis these are the areas you want to look at, in order as they pertained to my experience. This might be worth (attn: mods) placing on a sticky.

1. Electronic Throttle Assembly (Bosch type). Internal wear of the stepper motor reduction gears means the throttle plate does not always fully return to idle stop position. Cleaning the throttle body will not help. It sometimes runs lean at idle with intermittent DTCs for MAF and Long Term Fuel Trim (rich). You may also see intermittent DTCs while cruising for LTFT both lean and rich and MAF. Sometimes the car will start/stall, start/bad sputtering idle, or (when cold) start directly to low idle without revving up. Don't buy used ETAs, they're likely to have the same problem to some varying degree or will go bad in a relatively short time. My assessment on these Bosch ETAs based on the wear I saw in mine at 85k/10y is that they can counted as reliable for about 50k-70k miles and should probably be replaced on that approximate schedule if you expect the car to continue run 'like new' and pass emissions (if testing applies to the area you live)

2. Clogged/dirty injectors. Fuel not adequately atomized. Address as appropriate. Also check fuel pressure as part of a general fuel system diagnostic. Pressure at key on/engine off should be near 60PSI. Engine running at idle should be around 43-45 PSI. While accelerating pressure should vary between 45-60PSI with a correlation to hard acceleration/WOT to higher pressures. But for purposes of diagnosing excessive idle vibration just make sure you see stable pressure in the low-mid 40s at idle.

3. Resistance at ring terminals to coil pack grounds. Weak spark. Address as appropriate. The wire crimps at these ring terminals can be soldered. Due to oil contamination you'll want to use a paste flux with a brush found the plumbing section at the hardware store with silver bearing *lead free* solder (lead sublimates at under hood temperatures: you'll again have problems with these grounds someday). The little bit of flux in 'flux core electronic solder' won't be enough to clear the oil and get a good connection. Oil can also seep past the weather pack seals of the coil pack terminal connectors and cause problems both with the terminals and the terminal wire crimps, be aware.

4. Engine/chassis/battery grounds and main B+ (between battery and engine firewall). Check these for voltage drop. Replace/repair as necessary.

5. Engine and subframe mounts. These get blamed a lot. I'm not sure (in most cases) they are responsible. Worn engine mounts bad enough to transmit noticeable vibration will get noisy when selecting between reverse and forward gears and/or clunks and rattle while driving. Bad subframe bushings will result in sloppy steering, wheel alignment drift + wandering on the highway. If you're not experiencing any of these symptoms put these at the very bottom of your list.

It should be noted: my impression is that these cars are designed to give a 'light feedback' through the steering wheel -- just enough to alert the driver to any uneven roughness or a miss. Yes you can feel it, but generally will fade into the background/not command your attention while sitting at a stoplight.

Little more testing/driving today monitoring live data. Fuel delivery/FPA issue does appear to be fixed. 61psi at key position 2, idle and part throttle cruising 42-44 psi, spikes up under hard acceleration (I saw 51 at about 50% throttle). Roads aren't good enough today to do a WOT and hold it there I suspect if I did it would spike higher as it's supposed to.

Discovered this morning (little rough, hard start, 2 tries) kicked the throttle quickly a couple times and got smooth/normal idle. Did notice some surging and non linear pedal/power response.

I don't know which number on there is the date code. (see attached pic) No yellow sticker. Not sure that all applies to an '06?

If it does, was that an open ended recall or a "warranty extension" (likely on my own on an '06/now)

Edit: pressure at idle = 43.5 is normal. Knew it was a PWM pump assumed it maintained constant pressure. See "learning experience" reference below. You can skip the bulk/paragraphs to the live data does anything stand out I don't really know this car yet / what those should be.

In about a year or two I'll know this one in better than many dealer mechanics (so many of which are just following the functional equivalent of a flow chart but don't barely understand how any of it actually works).

Might be more to this than I thought, but maybe not. That 15 miles of excellence was coming out of a heated garage now that I think about it. I didn't check the pressure at that time I thought that was "done". Idle quality degraded to "hard but smooth" thereafter. Now one day later, parked outside, even colder, and 30 more miles, though the pressure reading isn't fluctuating erratically as it was before replacing the FPS and filter, diag tool shows pressure (steady) at 43.5 psi which is low. Idle quality also a bit rough until the engine bay warms a bit (was doing this-not new today). Note "hard but smooth" as I describe applied to nearly all of the '04-'07 S60s I test drove back in October/November-- you know, the steering wheel/chassis while standing in gear with the brake feels..uh..Stimulating (test drove 5, the only one that "purred like a kitten" in this respect was a '06 with 35k miles that looked garage kept (history showed Volvo dealer service through all 10 years/one owner). All the others had varying mileage and histories between 55k-110k) and were all more or less equally "stimulating" at a standstill. This one was in the middle (between the 35k one, and all the others)

My mistake on the first post: I had seen/confused information regarding other model years and have since corrected my knowledge that the EFI damper *is on the rail* on this one.

The times I saw pressure at normal (before the FPS/filter change, readings were erratic but peaked at 57-59psi) was when temps were well above freezing. I'll nail this eventually. I've dealt with far worse over the years ('95 Cirrus!). However, yesterday for that short bit the car demonstrated it is still capable of purring like a kitten.. the reassurance being when I do nail this down it will be obvious.

These are the live data I have access via my scan tool (elm327 to a laptop). Software I am using is somewhat limited but spits out the basics. Doubt it, but if anyone with more experience with these specific models can spot a specific combination of values that spell "eureka!" you might save me some time. (I'm new to Volvo, but fairly competent overall, every make/model presents "unique issues" and thus a learning experience). I haven't paid garage mechanic since around 1990 I've always been able to sort things out (sometimes with a bit of time and hair pulling a '95 Cirrus comes to mind).

**cold start, idling in park**
Fuel System 1 Status, closed loop
Fuel System 2 Status, unused
Calculated Load Value, 22.0%
Coolant Temperature, 107F
Short Term Fuel Trim (Bank 1), 25.00%
Long Term Fuel Trim (Bank 1), 3.13%
Fuel Pressure (gauge), 43.500 psi
Engine RPM, 668 r/min
Vehicle Speed, 0.0
Timing Advance, 5.0 deg
Intake Air Temperature, 37F
Air Flow Rate (MAF sensor), 0.6 lb/min
Absolute Throttle Position, 13.7%
O2 Sensor 2, Bank 1, 1.275 V @ -92.19% s.t. fuel trim
Time Since Engine Start, 0:4:19
Distance Since MIL Activated, 0 miles
Warm-ups since ECU reset, 52 (I didn't do this likely was the dealer or previous owner/auction)
Distance since ECU reset, 1566 miles (subtract my miles leaves roughly the distance between auction in Ohio -> dealer in Indy where I found it)
ECU voltage, 14.000 V
Ambient Air Temperature, 18 F

Stored PIDs 3,10,11,29,30. Doesn't tell me "when" or the DTC when the snapshot was stored.
CEL not presently lit

I haven't yet ruled out the Damper and might open the rail to reintroduce air (remove the FPS drains the rail, restart, observe) but this time do it outside/good cold start. Mileage is definitely off. It got 37MPG on the highway drive when I drove it home from Indianapolis (100 miles). Since this started about 10 days ago I'm getting 28 at best highway, stop/go is awful, except for that short period of 15 miles/minutes where it was back up. There's no telling how fluid hammer might affect the reading off that sensor. In addition to peaking high, the rebound would be low, especially if it times just right with a subsequent injector pulse. I should probably pick up an old school gauge. Tools for me generally get bought if I need them. Fuel delivery problems I've dealt with on previous vehicles were "all or nothing", or more obvious (leak, sputters at WOT, bad ground, pump works again if you whack the bottom of the tank, etc.)