Idles high or low; trans? radiator?

i have an '00 deville with 152,000 miles. sometimes when i try and start it it wont idle so i have to gas it for a little while then it will idle. but then sometimes it will idle high at like 1000 rpm's and feels like its accelerating on its own. even while driving the rpm's only go down if i come to stop in drive but then when i put it in neutral the rpm's go up to like 1300. i dont know if its the cold weather or needing a new radiator or transmission. ireally have no idea. any help would be very much appreciated.

I don't think that the radiator or transmission is where to be starting to cure an erratic idle. Start looking at the traditional poor idle areas. Spark plugs and wires, coils and fuel. The car will idle higher in very cold weather. Here in Toronto it is -10 to -20 and mine would idle at about 800 to 1000 in neutral right now until it warmed up then it would settle at about 650 in drive or about 800 in neutral I would say.
 
While a poor idle seems like an easy fix and it probably is it won't be cheap. A fuel filter is $25, plugs are $130, wires $240 a set, coils are $90,. Mine was idling rough and bouncing between 500 and 800 RPM. I started with plugs and fuel filter and it got better then the really cold weather hit and it was backfiring and stumbling. Had one bad coil with rusted terminals and change the wires. Did all this over the course of 6 weeks or so. Now I can't keep the front tires from spinning.
 
Of course if you have a trusted mechanic take it to him and put it on the computer, that will isolate the problem for sure.

Hey 10E:  A lot of the time the map sensor is the problem with erratic idle. You could also be encountering a faulty ECM. When it comes to electronics the fix is usually not cheap....Caddies are fun aren't they????
 

yeah, I had the same exact thing, I thought I was the only one that paid 240 for a set of damn wires

Genuine GM parts! Tough to buy anything else for a Northstar.