With the GE CF6 engines, the engines will be trimmed together as long as the throttle levers are within approx 1/2 knob width of each other and the Autothrottles engaged. if one throttle is moved outside the 1/2 knob limit, that engine will be set at an N1 proportional to the throttle position, and the other 3 will be trimmed together. That out-of-trim engine throttle will still be adjusted linearly along with the other throttles.
So, if you set 1 throttle to idle to (for example) clear a stall or troubleshoot high oil temp, that throttle will move off the idle stop as the other throttles are adjusted higher, and go back to the idle stop when they are brought back. The only way to keep 1 engine at a constant N1 is to disengage the Autothrottles.