97 Taurus rough idle problem

This is really general, i know, but i've been trying to track this problem down for a couple of weeks now..
97 taurus GL, vulcan 3.0 engine. it's got about 160km (100,000 miles) on it.
It has an intermittent rough idle, it's more noticeable especially when the engine is cold, or if the A/C is on. I replaced the plugs and wires, that didn't change the condition at all. I've also noticed it sometimes takes a few seconds longer to "catch" when cranking the engine. This leads me to think it could be a coil issue? The car is quite well maintained as far as scheduled service goes. I don't know if this is related, but the trans seems to be shifting harder then it used to, the idle and the shifting seems to have cropped up at the same time.
No codes, no check engine light, nothing. I'm just a little worried that when the weather turns cold here (Ontario Canada) that it'll be more then just a rough idle, and i hate doing repairs in -40 weather...
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Teknical opined in

it's probably not the coil... hard to start when cold and damp (external arc), or bogging on acceleration (internal arc), is a good indicator of that.
If the idle seems to hunt... or higher apparent rpm with a miss, it's a bad mixture at idle which would point to a small vacuum leak. Check all the vac lines coming off the manifold.. esp plastic tees and connectors for cracks. Had that problem with my 95. Replace with brass from HW store.
Also check TPS, fuel pressure regulator.. A bad TPS also might affect shift.
Both affect starting.
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Really? a bad TPS affects starting? I honestly wouldn't have thought that.. Thanks for the heads up
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