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OK, I rebuilt the motor in my car, which is a 99 civic ex with auto trans. I used a Y7 block cause i got it real cheap and put the Y8 head on it. When you start the car up it sounds fine and starts with no problems. But, when I try and drive it, it will run fine at first and then will start acting up. When it starts acting up if I pull up to a stop sign or red light the rpms will drop almost to 0. When I press the gas down it will slowly pick up speed, I mean I could push it through the intersection, when pulling away from a red light, faster then it will. Also, it won't shift from first gear until it gets to about 4500-5000 rpms. It does this through 1st 2nd and 3rd gear. I haven't gotten any further then 3rd gear since I haven't driven it far. I checked the trans fluid and it's fine, I had just filled it after putting everything back together. And i'm not getting on it, just regular driving. It only seems to do this after it starts to warm up. If I start the car up and just start driving, it runs fine until the temp gauge gets to about the 1/4 mark. The car ran fine for a few weeks after the rebuild and one day it wouldn't start. I checked everything out and it looked fine, just wouldn't start. Then the next day I went out and it started up just fine, but that's when the problems started. Also, it keeps throwing code P0325 for the knock sensor. I bought one from the dealership and put it in and the code went away for a few, then came back. I have checked all the wiring and everything looks good. Any info at all would be greatly appreciated.

Thank you