pull off spark wires, do one at a time off, and note the idle change if any. A bad plug, or spark wire or cap will give little or no change in idle rpm when disconnected.
If all six give same result, then problem is likely not isolated to a single cylinder, and thus may be an issue of bad coil, vad coil ground and power input, bad center cap wire or electrode, etc tgat effects all six cylinders.
You may also wish to remove the plugs and inspect condition, note differences.
Assuming you got a wrench for this.
If you got an ohm meter, check the spark wires cap.
If volt meter, check voltage to coil primary when operating, note voltage when revved.
at idle, listen to engine near plugs, wires and hear if there is any snap noises, or crack noises, basically an arc jumping is what you try to hear, an arc from a cracked plug, or busted spark wire, t will be a tick ticktick noise at idle. if pitch dark, look at the sark wires at idle, look for flashes of arcing, you should see no arcing. I have found defects sing all these methods
Could be you got a bad plug, sometime one is damaged, or maybe a spark wire gave up when removed last, or some connector got jostled around.
could be an injector is clogged or not getting proper command to fire. remove each injector electric plug, one at a time, and note idle speed change, if no change, then that injector was not firing before.
sure you could have an intake leak, but that is not going to be related to a recent plug change. You can test for intake leak with aerosol spray can of flammable carb cleaner, at idle, spray at suspect leaks, around gasket, etc and note for idle speed change.
good luck
