I installed the new fuel injecter got everything all set and it started first key turn.

Drive much smooth. But Stil has a slightly low rpm. and then about 2 hours later it wouldnt start on the first try. i had to give it some gas. and now it backfires a little bit after i release that gas around 2500 rpm's. Any ideas? spark plugs anything?

 

Pulled any codes?
Tune up done?
Engine coolant temperature sensor might be the culprit.
Good luck.

 

did you change all of the injectors or just one?
i have heard that some aftermarket stock injectors will only work if all are replaced. has something to do with the voltage returned to the ecu.

 

I'm thinking loose distributor

 

the fuel injecter is spraying some gas through the seal now up and onto the engine. I am pist. Would it be because the spark plug isnt firing and the gas is overloading? or do i need to pull it all apart and put new o rings on it... i got all the parts through my nissan dealer and they took my vin so i know its the right injecter....

 

i'd go with because you didn't use a new o-ring.

 

"Would it be because the spark plug isnt firing and the gas is overloading?"

To answer that question, no. Any unburnt fuel gets blown out the exhaust and at worse will cause a backfire when it builds up sufficiently.