I’ve got a misfire problem with my Focus. It started about a month ago and did not trip a code until last week. It stumbles on acceleration between 2,000 and 4,000 rpms. It is only a slight stumble and although noticeable, it does not impede driveability much. Last week I was able to get it to finally trip an OBD code. P302 - Cylinder 2 misfire. I changed the plugs and wires with no effect. I thought I had it narrowed down to the coil or injector until my wife noticed a new wrinkle.
Under normal driving conditions the misfire is annoying, but my wife found that if she turns on the A/C, it is undriveable and will not accelerate past 30 mph without some patience and a neck brace for the bucking. My first thought was the A/C compressor was freezing up. I turned off the A/C and left the blower on and it would not stop missing. I turn off the blower and it smooths right out to the annoyance I described first.
Right now I drive the car without A/C and blower whenever I accelerate. If I’m going a steady speed, all is well and I can run the blower and A/C.
I thought I had it narrowed down and I was going to buy the $80 coil tomorrow, but now I just don’t know. Can anyone help?