well first of all the motor is a b20vtec. It's running great except for a few things. When it first starts (cold) it no longer idles at 1500rpm but 2500 instead and then gradually goes down to about 800 or so rpm. Not only this but the car will die at every light until it gets REAL warm like 10 minutes after starting it. I think it may have something to do with either the IAC or the cold start valve.

Next and lastly,
when under severly sudden heavy breaking or accleration a fairly loud "thud"
can be heard as if something hits the bottom of the car. It usually happens right upon breaking or dropping the clutch at high rpm. any help is greatly appreciated. TIA

 

This is a dumb question, but have you tried resetting the ECU yet?

Have you checked if the thermostat was functioning properly?