Congrats on having a really, really nice car there, Erick!
You'll likely always have either P1000 or P1111 stored in the OBDII (On-Board Diagnostic system, version II). If you have P1111 then you should be happy. It's a good code.
The P1111 code indicates that all engine tests have completed by the computer, and everything is okay. The reason it is there is because the car has to be driven for a while before all tests are complete after a DTC (Diagnostic Trouble Code) reset or battery reconnection.
(P1000 means those same tests have not yet been completed, it does not indicated a problem, just the fact the 'puter has a bit more work to do - for whatever reason)
The P0172 code is a different beast, however. It can mean the following:
Restricted air filter
Leaking fuel injector(s)
IP Sensor fault (high fuel pressure)
EFT Sensor fault (high fuel temperature)
MAF Sensor fault (high intake air flow)
HO2 Sensor(s) (1/1, 1/2) harness wiring
ECM receiving incorrect signal from one or
more of the following components:
ECT Sensor, MAF Sensor, IAT Sensor,
IP Sensor, EFT Sensor, TP Sensor
1) Change out the air filter, and use the code reader to clear the code. The code is telling you one of the "banks" (sides of the engine) are running a hair rich, that's all. An air filter that is a bit restricted can cause this.
(While you are at it, change the oil and filter, too - yours is a World Class Automobile, treat it as such and keep it fully maintained, Erick! I am writing this to you on a Saturday. Go outside and hand-wash that pretty baby, today!)
If the code returns promptly...
...the usual reason for the code is crud - usually invisible crud - on the MAF sensor, an easy fix. If everything else about your car's performance seems okay, and this code re-appears after clearing it from the OBDII a few times, then and only then take the step of cleaning the MAF (Mass Air-Flow Sensor).
(if you Google the price of a replacement MAF Sensor for your car, you'll understand why this is not the very first thing you want to do)
The MAF Sensor is the honey-comb thingie after the air filter, and before the engine. It does a p**p-load of things: it tells your Jag's MAIN computer (your S-Type has 6 or 8 different computers on-board!) what the air temperature, oxygen content, humidity, and likely a few other things, too, are - many, many times each and every second you are driving down the road.
Go to a NAPA Auto Parts store (or other "Quality" auto parts store), and buy the single BEST brand of MAF Sensor Spray Cleaner they have. Do NOT "skimp" and buy a WalMart or similar brand - they are NOT all created equal.
DO NOT, UNDER ANY CIRCUMSTANCE, USE "CARBURETOR CLEANER"!!!
Disconnect, unplug and pull the MAF Sensor out from "under the bonnet". Make sure you use a nice blanket or something to lean on and rest against while working on it (excuse me, it's an English Motorcar, so I should say "whilst working on it"), to make sure you do not scratch the paint of your Jag.
Take the MAF Sensor across the yard, or out of the garage (anywhere, far far away from the car) and spray the cleaner through it, following the directions on the can to the letter.
(if you accidentally mist the spray onto the car, you will screw up the paint job something royal. You do NOT want to do that: everyone knows, if you mess with the paint on a Jag, God Himself will not allow you into Heaven)
Just clear the code, Erick.
If it comes back, or if you have"drive-ability" problems, then you can deal with the MAF Sensor. Don't get too terribly hung-up when your Jag throws you a code, they are want to do so.
(kitties are temperamental beasts, all)
Post Script - Join (or at least Bookmark) http://www.jaguarforums.com
They will help you with EVERY problem you can (and likely will) encounter with your beautiful car.
Post Post Script - one of these days, your Jag will likely jump into "limp mode", scare the heck outta you, and you will get a screaming number of OBDII codes. It will usually happen when you "need" the car most (in traffic), as you accelerate. It is a "false call": it will be a simple vacuum leak. Pull over, turn the car off, and restart it (yes, you can do it 'whilst' rolling, but the steering wheel will lock on you for a moment). If you can readily find the leak, a bit of your girlfriend's bubblegum will fix it!