Rough Idle on a 4.0 liter '92 Explorer

Actually it's more of a cough and it is very minor. It is minor enough
that I don't get an engine warning light, and it passed my last state
emission check.

It only happens when in gear and stopped. If I place it in neutral or
park, or am driving, I don't feel it. Cold or warm (weather and engine
temperature) it's always the same.

I've:
replaced the fuel filter
replaced the plugs
replaced the plug wires
checked the timing
flushed the injectors

and none of those seemed to make any difference.

I've checked the history of the group and don't think I've seen anyone
else with a similiar problem.

Any ideas? Thx in advance.

im responding because the 92 takes a hot plug 52.00 at ford, napa 7.99
aplug
i noticed a big differance with original plugs
plugs are AWFS 42C

Hi,
In USA you can also try rockauto.com
i bought plugs for my 1998 explorer and other parts for my husband US olds
cars (he collects them), price is OK.
plugs motorcraft 3.90 $ and in france 26 euro each (about 32 $)
have a nice day
claude from france