Rough runing on cold start up

My 95 xj12 runs rough when cold. I have to coax it to stay running. But when it warms up it runs fine. Any suggestions on where to start to fix the problem

it’s been years since I owned a V12 but this reminds of a problem with the vacuum solenoid thing over the LH side of the engine. Members with more recent knowledge will supply the name… this is a vertical unit containing a piston which rises under vacuum supplied by a solenoid and admits extra air into the LH intake manifold. These things get stuck, either closed or open, creating problems with cold start. It is supposed to close once the temp reaches a certain level, and doesn’t activate at all for a warm start. If it’s stuck open, the engine will try to race as soon as it gets a bit of heat into it. If it’s stuck closed, the engine will be unable to idle when cold. Unless of course they figured out how to remove it on the later 6L engines…