If you read that link TSB I posted, you can see where it says the causes:
This condition may be most noticeable when the engine is restarted following a prior 10 to 20 minute heat soak in hot ambient conditions of approximately 32 C (90ºF)or higher.
This condition may be consistent with short city stop-and-go driving trips and can be aggravated by the use of fuel with a high ethanol 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 vapor to form within the injector. This in turn may cause a momentary misfire of cylinder #3 until the fuel vapor is cleared of injector #3.
The insulator sleeve lowers the injector #3 temperature to a point below which the fuel will not normally vaporize.
1. If vehicle exhibits a rough idle, and if a misfire of cylinder #3 is observed following a 10 to 20 minute hot soak, perform the Repair Procedure.
In other words, It will only happen when it is really hot under the hood. Like after a 10-20 min drive/shutdown period.
I would see if you can make that shield on your own, or you may be able to buy it from the dealer (as someone noted in your origional thread), the PN is 56028371AA and it should not be too expensive, the instructions are in that TSB I sent you.