problem with 98 isuzu rodeo

hello, i have a 98 isuzu rodeo that i am having a constant miss when at idle on the middle cyl driver side. i have swapped coil packs with front cyl and when i unplug wire feeding coil pack result is still the same at idle. it doesn't appear to have any power loss when reving engine but has a sulpher smell when at idle. does this sound like an injector problem or a gremlin? thanks

what is the history of the timing belt change? Maybe the belt slipped?

unsure bought rodeo used with 68k miles on it it now has 89k on it. i wasn't sure if it had timing belts or chain?

what kind of spark plugs are in it?????
They are particular about what you put in them, seem to run best with Nippendenso plugs.

I have Bosch platinum plugs gapped.040 thous. installed 2 months ago. approx 2,500 miles to go.