I recently bought a 2007 CTS 3.6l with a bad engine. Picked it up for $2500 with 83k on it. Went to car-part.com and bought a 2009 3.6l engine with 56k on it for $1300 to install as they said it would fit into the vehicle. Before installing the engine on the car I got a new timing kit put on, water pump, belts, etc. Now the engine is in the car and it will start and idle fine but once you press the gas, nothing happens. The only thing that was swapped from the old engine was the intake as it was slightly different. I know that in 08 they changed a little bit of the timing system (chains, etc) so I'm wondering if possibly the ECU would need to be changed to compensate for the difference? My mechanic said that he thinks it's just the throttle body, it's making clicking noises and it looks like someone has went into it before, as it was missing some of the clips that hold it together. Now on the other hand, sometimes it will not start at all unless the battery is disconnected and reconnected. Something is telling me this is more of an issue with the ECU.. Anyone have any ideas? Please help!! If it's not the throttle body, that's $220 down the drain!!