Engine Bucks and Misfires When Cold
I have a 1997 Ranger 4x4 4.0L automatic. I have replaced the spark plugs and wires, fuel filter, and PCV valve all within the last 2 years. I also installed a Screaming Demon coil pack and gapped a new set of plugs to 0.063 two years ago. Twice within the last week or so when I started my truck in the morning it ran real rough, like it's misfiring or only running on 5 cylinders. It's misfiring so bad that it makes my truck shake and also bucks when I drive it. It does this when it's idling, accelerating, and cruising and in all gears, but seems to buck worse in 4th and 5th gear. What's weird is that it goes away shortly after my truck warms up and then my truck will run fine. It has done this to me once last week and did it again this morning. My truck has not thrown a check engine light unfortunately. I have read up on possible issues and I think that it might be a bad EGR valve, a fouled spark plug, or a bad fuel pressure regulator. It seems most likely to me to be a bad EGR valve, but I would assume that it would throw a check engine light. I'm just looking for other opinions before I spend the time and money on replacing parts while trying to chase down this issue.