2003 Mitsubishi Eclipse Idle

I purchased a 03' eclipse about 8 months ago. It had a blown engine, so I swapped it out with a engine from Ebay. Before I got the engine the person I bought the car from informed me that the engine I bought came out of a Automatic Eclipse. Mine is manual.

My car runs and drives great once it's warmed up. My problem is that if I start it when the engine is cold. The engine will immediatly rev up to 3000 rpm, and then idle down real slow. After about 20 minutes I get a P0421 code. I found that if I disconnect the air intake hose from the Mass air sensor. The car will start up, and Idle perfectly.

I've already replaced the Idle Air Control motor, and Mass Air Sensor.

Thanks for your time.