The new timing belt should not be the cause of the symptoms described.
The burning oil smell could be oil or trans fluid splashed onto the exhaust. Check for leaks or just oil/fluids splashed onto the exhaust while repair work or trans flushing were being carried out.
The humming noise could be due to failed trans mounting or improper installation resulting in vibrations being carried into the cabin.
This part is a little confusing, do you mean the engine is surging when stopped?
" Finally, it seems to idle irradically, high idle when driving, slowing down and speeding up and very low idle when sitting."
The erratic idling could be due to the battery being disconnected during repair work and it would go away after the computer has reset itself after some running.
Other possible causes are faulty Idle Control Solenoid, leaking vacumns, timing belt out of sync ( not likely since you mentioned better performance), insufficient coolant.
Wednesday, September 15th, 2010 AT 1:00 PM