My Focus was shuddering, hesitating and stalling in 1st & 2nd Friday
night, I drove it to the Mechanic Saturday morning and it wouldnt
start!
He had to replace the Ignition Coil pack $310 it was cracked. My Focus
is now 5! Last month I had to replace the Thermostat Housing $250.
The mechanic said one of the wires is bad as well, the mechanic said
he rigged something with the wires but it is only a temporary fix. He
told me that Ford may make a part to protect these wires? And he will
find out tomorrow? Any idea what he may be talking about? Or is he just
trying to pull a fast one?
Thanks in advance for any help you can offer.

I dont know if this will help you at all, The post below was copied for
you from the Ford Fanatic Forum...This is some guys story from March,,,

Here's my sad story. I just bought an A4 and I'm driving the Focus the
remainder of the winter to keep the Audi off the road when its really
nasty. After I change the insurance and plates over to the Audi, I'm
giving the focus to my sister. Saturday I replaced the el-cheapo intake
and installed the factory one so that she would have an easier time
with maintainence. For any focus owner, you all know this is a 5 minute
job. Got in the car, fired it up and it was idling a little rough. I
decided to reset the compy, so I unplugged the battery. Fine, come
back, plug it up, back it out, put it in gear - NO POWER. We're talking
bogged down nearly stalled, takes 5 seconds to cross a two lane
intersection. bad. very bad. So I drove it around hoping it would throw
a CEL, and it didn't. So I took the intake off, cleaned everything up,
checked all the wiring, put it all back together, tried it again, same
result - crap. Thankfully it threw a code this time though. P0351 -
ignition primary/secondary failure - wtf? How in the hell does swapping
out the intake make the ignition give up the ghost? Okay, so I went to
autozone and got a new ignition pack - swapped it out, all was well.
The car was snappy and responsive again - end of story? no. This
morning, in the pouring rain, I was driving normally to work, got to
the freeway and the bloody thing started doggin AGAIN and immediately
threw a CEL. So I babied it back to the apt and swapped the plates onto
the Audi and drove that in (not registered, insured, or plated -  ). I
am now dumbfounded. do foci have coils? maybe that went bad. Perhaps
there was corroded wiring in the signal wires into the ignition and
when I moved the MAF sensor wire around it broke.

Oh, another thing, it seems to be heat sensitive. starting temps engine
runs fine, mid temps, runs like its firing on two cyclinders, warms up
and runs fine(?) I can't garantee that last one, it came back right as
I was pulling into the driveway but it was done for the day by then. In
that transition period, it acts like its sputtering between high and
low power, like some jerk is sitting at a switch throwing it back and
forth, so I get intermittently thrown back in my seat then lurch
forward as it slows down.
2 days later...
I figured it out on my own. Turned out to be the wires that provide the
low voltage signal to the ignition. One of the wires that runs into he
back of the wire harness that hooks into the front of the ignition had
corroded to the point of failure. I had to chop the wiring harness off
and crimp female spade connectors to the wires and then hook them onto
the male leads in the ignition. A little rigged up but it will work
until I get a scrap yard harness and splice it in.