My car is a '94 Honda Del Sol with a B18C1.

First problem is the unstable idle. It's been there since I bought the car almost 6 months ago. Never really bothered me but it's starting to get annoying. It'll rev from 1000 to 1500rpm once it reaches operating temperature. It'll usually die off sometime later, but sometime it'll go on forever. When first first starting up it'll rev up to about 2000rpm and drop to 1500rpm, where it'll stay until it reaches temp. I've searched this many times and this problem seems fairly common. Tonight I took off my throttle body and cleaned it good as new, then took off the IACV and cleaned it out best I could. Didn't seem to dirty to begin with. Put it all back together and the problem is still there. I fiddled with the idle needle some. Unplugged the IACV and tried to get it around 500rpm as I read in a previous post. Even with the needle all the way in, it'll only go down to 800rpm. This becomes 900rpm when I plug the IACV back in. Turning on accessories will cause a momentary drop in idle, and off a momentary rise. Is it ok to leave the needle all the way in until I find a better solution? This leads me to believe I have a vacuum leak. What's the easiest method to find a leak? I'm going to give the propane method a try unless someone has a better idea.

Second problem is some misfiring. A few days ago I decided to wash out my engine bay. I was trying to be careful not to get any water where it shouldn't go. Car ran like crap afterwards. After a couple trips it felt like it was misfiring bad. I pulled the spark plug boots to take a look at the plugs and the holes down to the plugs were about half full of water in two of the holes. I was able to get the water out by jamming some paper towels down in there and the problem seemed to go away. Tonight after working on the throttle body and IACV I noticed the problem was still there. Unplugged the boots again and one still had water in it. Could this be new? Could coolant be leaking around my head gasket? I was pretty sure I got it all out the first time and I left the boots unplugged to let any leftover water evaorate out. It was too dark to see if the liquid had any color. Did I do any damage by driving with two spark plug holes filled with water? I'm really hoping it's not possible water could leak into the engine through the plug somehow. Can anybody confirm that?

At my exhaust tip there's some water droplets. This only happens when warming up. Could my head gasket be bad? I've kind of been suspecting this for a while. I also have some black soot falling out of my exhaust that I've posted about before. It seems like it's gotten more liquidy. It doesn't really smoke until you hit VTEC. The engine has around 75k miles on it. Is a head gasket an easy job for a first timer, and about how much do they cost?

Thanks in advance to anyone willing to share some advice and experience with me.