Idles fine, falls on its face when you open the throttle.

[standard235]

Could a coolant temp sensor cause the issue? I know my DSM had the ECT that went to the ECU fail, and apparently it isn't meant to run at -37F...

The car has the following replaced before issue:
K&N Filter
BWD Cap and Rotor (swapped yesterday by suggestion)
NGK V-Power BPR6EY-11's gapped to .044 (Also swapped after issue started)
Autolite Wires
New Fuel Pump and filter and tank
New ignition coil (I warranty swapped it and just got off work today so I'll be off to install in a bit)
New ICM (After issue started)

It's extremely strange because the smooth idle was a myth. I never let it idle long enough to realize eventually it would get incredibly rough and try to die.

If you turn the key and it fires, it will idle up smooth and come back down, sounding perfectly normal. It's like as soon as the PCM lets a sensor start varying fueling that it goes to hell. And it's definitely over fuelling because the plugs were wet when I pulled them. I don't think it's an ignition issue because every plug makes a beautiful blue spark now.

Unplug TPS, no change. Pulled VAF (and destroyed studs in process... m6x1.0 bolts ftw) and made sure door isn't sticking or anything. I bought a new TPS yesterday and it will be in today, any ideas before I install $70 worth of waste on the car?

[Flyin4stroke]

Idles fine, falls on its face when you open the throttle.

Verified timing? Annnd maybe fuel filter? Sounds like everything else is in good order. Does the car drive at all? Can you make it run by blipping the throttle?

As mentioned before the tps on these cars doesn't do much only tell the computer on or off. Basically wide open and no throttle.

[Movin]

Unplug the O2 and try it.

[standard235]

Timing is fine.

Issue started when the alt belt failed. Car died, jumped with pack to get the last 3 miles home. Got home, shut car off. Replaced belt. Start car and it runs. With a misfire. What the hell? Realize pos terminal on battery slightly loose. SHIT.

Tighten terminals, and no dice. I'm assuming the incredibly unstable voltage killed something electronic. Really hoping it isn't the PCM itself... but it's making more and more sense.

Forgot to mention I unplugged the o2 and it didn't change anything.

[standard235]

My issue is VERY similar to this thread. Like damn near identical.

http://www.fordfestiva.com/forums/showthread.php?34550-Bogs-stalls-won-t-go/page4&highlight=temperature+sensor

Guess a new VAF may be in order... I have a bunch of crap to return at AZ and get a Cardone reman so I may do just that (no JY nearby keeps Festivas )

[Movin]

Unplug the O2, remove battery neg and step on brake pedal for 15 seconds and then try it.

If it is still the same remove the plastic cover on the VAF and play with the arm to see if the idle gets smooth.

[standard235]

At this point, I would if I could get it to stay running long enough to do that

[Movin]

Might have to clean the plugs, they will only last 5 or 10 minutes if running as rich or lean as this engine may be.

[standard235]

Fuel pump o ring... never rule out something you've recently been through. Ring didn't seat so fuel pressure pushed it out enough to leak down. Car runs great again and I got to return the ICM/TPS I didn't need. $$$ to finish Aspire/Rio swap! Thanks for the help though guys.

[XFSE71]

"Fuel pump o ring "... low fuel pressure ... of course.