[Baprace]

2003 Focus 2.3 liter 5spd with 125000 miles, uses no oil, no smoke. I have been chasing a very slight throttle misfire/bucking, it occurs when my shift light comes on , my flaps are working. solinoids are good, I checked the injectors, installed new fuel filter, pulled the injectors the screens are clean, it starts well cold, and runs well when HOT, it's intermediate temperature when it bothers the most, give it any throttle to accelerate and the misfire/bucking is gone. The car runs very well when it is up to temp, mileage is good and I have checked for vacuum leaks and have not found anything, no codes. Any help is appreciated.

 

[Marde]

I have been fighting a similar problem, but you have a few key differences that make me feel you have something different going on. Strange you have the problem in-between cold and normal engine operating temp.

First check the PCV hose. If it is original, it must be bad by now. They crack and cause vac leaks and strange problems. Check or replace spark plugs, use AR103 copper plugs and set gap to .055. Check health of each spark plug coil rubber boot.

PCV Hose replacement thread;
http://www.focusfanatics.com/forum/showthread.php?t=212938