I did put a 4.0 tb on my 2.5 6 months ago and havent really had issues. It always goes to 2000 rpms when i start it but then goes down to 1000 or so after about 10-20 seconds. Now it is idling low and rough though. It gets down to about 500-700 rpms and vibrates a bit from such a low idle. What could be the cause and how can i fix it? Can i just rakse the idle?