i have and 03 ranger with 122000 on it, and since ive had it it has idled rough when sitting still. i recently took it to the shop to put it on the computer and they said i have a miss fire in 4, 6, and that it could be caused by either carbon build up or a valve problem. does anybody have any other ideas of what could cause the miss fires.ive changed the plugs and wires so far.

 

I would run some seafoam through the brake vaccum line. Then turn it off for about 10 minutes then start it up and drive around

 

why the brake vacume line?...and what exactly does sea foam do?

 

https://www.ranger-forums.com/forum2...hlight=seafoam

 

If you've changed plugs and wires the only other thing you could have is a coil pack or a fuel injector. I am going through exactly the same thing right now with my truck and I'm at less than 71k. I did a compression test on my truck and cylinder 4 is at 125 psi and the others are over 175 so I definitely have a problem with the exhaust valve not closing on mine. I ran sea foam two days in a row and it works well but it didn't fix the problem in mine.