Ford Repair: Ranger rough idle, pest control business, veicle

Question
Hi Brian,
I just bought a 1989 Ford Ranger plain jane type pickup. It had
some number decals on it, and I assume it was a service vehicle
for some pest control business.
It seems to have been pretty well maintained aside from the plugs
that looked like they were the originals.I was surprised to find
(8) spark plugs in this little four cylinder.I changed them and
thought that would smooth out the fairly rough idle.That's my
question.Is that just characteristic or what else should I look
for? Other than the rough idle when you are at a stop and in gear,the truck is just fine. Thank You for your time. Bill

Answer
rough idle on this veicle is usually caused by an egr valve that is sticking open a little or the valve that controls it not closing properly. other than that, this vehicle was not known for idle quality. i am unable to send a picture of the vlave but if you go to you tube or google. you can type " how to replace the egr valve on my "" ??? "" and you will see either pics or a video.