Well i just bought this van and was told the water pump was bad. So i replaced it along with the thermostat, belt, plugs, wires, and new battery. When i start it cold it doesnt want to start with out a bit of help with giving it a bit of gas. Then while it is running it is a hair rough running. If i slowly give it gas idle picks up then starts to drop so i give it a bit more and same thing. Then if i let off the gas to fast it dies. If i rev it up and stop to let it go back to idle it dies. But when it warms up it quits doing this. Another thing i know this van has sat for awhile not sure exactly mabey half year to year. So i was thinking the gas may be old??? Any ideas on this problem. Oh and i checked codes and just came back 12 which i think means lost power from me changing battery and 55 which i think is end of test. Plus one other thing the spedo does not work i thought speed sensor but it wasnt coming up in codes. Any ideas with these problems?

ok it is running fine now but the speedo still doesnt work. Iv checked codes and the only new code that i pulled was a 14 and from what i looked up that would be a map sensor. So i guess il pick up a map sensor tomorrow. If the speed sensor was bad could it just not show up in the codes or do i need to drive it around a bit for it to pick up on the speed sensor?