truck runing bad in the rain??

[cashmoney37]

i was driving home and it started to rain real bad and my truck started boggingand sounding like it was missin. i just changed my plugs and wires. somthing i did notice is my heater and a/c is stuck on defrost. i traced all my vacuum lines and they are all hooked up. but i do here hissing when i shut my truck of i hear it around the egr back side of the intake area. i cant find the leak,

why would the rain make it run bad? it has coil packs not distributor. its a 2000 5.0 mountaineer.

 

[firepop5]

If you hear a hiss, you probably have a vacuum leak. Check under plenum of upper intake manifold on drivers side. There is a fitting there that should have a rubber cap on it. These caps deteiorate with age and can fall off, leaving a major vacuum leak.

 

[cashmoney37]

cool, i will check there. would a vacuum leak make the truck miss and pop in the exhaust?