XJ shaking sometimes on start up?

Lately about one out of five times I start my XJ it starts shaking for about 10-20 seconds then the shaking stops and it starts running fine. It never does this when I'm driving, just when I start it sometimes. It was time for new spark plugs, so I replaced those yesterday. I thought that might alleviate the problem, but it did it again today. I'm thinking it might have something to do with the amount of fuel getting to the engine during starting and then idle after. Maybe the fuel pump is going out?
I have some more work to do on it tomorrow (replacing radiator and heater hoses that are cracking, and then replacing the EGR valve) and it would be nice to get everything I needed done at once but i just don't quite know what the issue is.
There are no major mods done to it except exhaust (cat back) and 4in lift. No engine work...yet.

Anyone have any other ideas of things I should check?
The XJ has 98000 miles on it, btw.

Is it shaking like its starving for fuel? Or it is shaking like its missing? Could be a bad motor mount?

I did think of the motor mounts. Hmm...I've never had a vehicle do this before so I don't necessarily know what the difference in shaking is. Could you please explain?
Also, is there a reason I can't find EGR valves for XJ's anywhere? I keep getting told to go to a dealer...

The shaking is probably vapor lock. 1803103 - 4.0lt Rough Idle After Start Following A Hot Soak Date: 09/05/03 Model Year 1999-2004 Description Note: This bulletin involves the istallation of a fuel injector insulator sleeve.

Details : Customer may describe a 20 to 30 second rough idle following the restart of a heat soaked engine. This condition may be noticeable when the engine is restarted following a prior 10 to 20 minute heat soak in hot ambient conditions of approximately 32 C (90 degrees) or higher. This condition may be consistent with short city stop and go driving trips and can be aggrevated by the use of fuel with high ethonal content. Depending upon various conditions a MIL may occur due to DTC P0303 - Cylinder #3 Misfire.

This condition may be caused by heat from the exhaust manifold that following engine shut down migrates to the area around injector #3 and causes fuel vapour to momentary misfire of cylinder #3 until fuel vapor is cleared of injector #3 temperature to a point below which the fuel will not normally vaporize.

If the vehicle exhibits a rough idle, and if a misfire of cylinder #3 is observed following a 10-20 minute hot soak, perform the repair procedure.

Parts required:
56028371AA Ignition Wire Shield

Repair Procedure:
1. Cut insulator sleeve, p/n 56028371AA to make two (2) insulator sleeves about 25-33 mm (1") in lenght
2. Install one sleeve around injector #3, with the slit on the upward facing side of the injector. Install the other sleeve with the slit on the downward facing side of the injector.
3. Confirm sleeve is flush to intake manifold surface around injector.