Haven't posted on here in a while but I have a problem. I have a 55 Olds 88 that runs great. However, Since I bought it 4 years ago it always idled real high for a few minutes before dropping down to a normal idle after start. The time it needs to run before dropping to a normal idle has gotten longer, and now it can go 15 minutes like that! Sometimes it will eventually drop if I keep stepping on the gas, or it will just drop by itself. starts easy (even after sitting for 3 months) and runs fine otherwise. Could this be a choke issue or vacuum leak? Thanks, I'm not much of a mechanic!