does it now idle or do you still have to hold the throttle down a bit or allot?

If it was running perfectly before the transplant then you must have missed something or bumped/broken something.

Start checking all the plugs/connectors for a good CLEAN fit, check all the earths as well especially the one at the ignition modual. If you think it is running on 3 cylinders then one by one dissconnect a coil pack or injector lead to determin what cylinder is at fault and if it is either a fuel or spark fault. Check the Air Flow Meter (in the intake piping) make sure it is clean and the plug is clean and fitted well. Check the wiring to the cold start/high idle circuit, its just near the plenum.

Hope this helps dude.