I have a 94 f150 w/ inline 6 engine. has aprox 70,000 miles on it. was missing when traveling at a constant speed, not when idling or accelerating. i replaced the plugs(motorcraft), gapped them, replaced the cap and rotor, installed new plug wires. now the problem dosnt occur when traveling at constant speeds, it happens when coming to a stop or when your not moving and the transmission is in gear.( auto transmission.) any suggestions where to go now? Thank you for your time!

 

So when it is idling now. If that is the case, I would suggest checking the IAC (Idle Air Control Valve). Could be gunked up, or simply starting to go bad. If that is not the case, let me go out on a limb and suggest checking vacuum hoses. Wouldn't know where to start if that. I hope this helps. I'm not very familar with the 300 I6, so going off of experience.