99 F-150 - hard to start

When I try to start the truck, 4.8L, V8, you have to push the gas to keep it running & take it off quickly, it will either stay running or die. Sometimes it takes several times to do this. Once started, no problems, all gauges fine, etc. But it is every time you start it. 113,000 miles, had 100,000 tune up done on it w/ no problems. Also, water dripping from back tail pipe. Any ideas?