I have a 1998 Ford Ranger XLT 2wd 3.0L manual transmission. I got a tuneup with new plugs about 1,500 miles ago. I don't drive a lot anymore, so that was about a year and a half ago. Over the last few months, it had been running rough. Had gotten to the point of a very noticeable miss, and loss of power on acceleration. Worse when cold, wet. I didn't think it had anything to do with spark, as the plugs had just been changed. Mechanic told me it might be a vacuum leak. The other day, I popped the hood, heard that sparking "tick" sound. I knew it had to be the wires arcing somewhere. I pushed them all down hard onto the spark plugs. None were noticeably loose, but it was just enough to make a difference. It now runs like brand new. Just checking the seating of the plug wires on the plug. Saw on one forum that it's a common thing with DIY tuneup's. So even if you pay a mechanic, check it yourself. The difference is night and day. I see a lot of forums about rough idle. Checking the plug wires might want to be the first thing on your list