My windstar about a month ago developed a missed detected in #2. It also had a rattling noise coming from the backside of the motor, a weird sound coming from the plenum almost like a popping noise.
I tried all upgrades even the valve cover upgrade, coilpack, plugs,plug wires, o2 sensors and nothing made it improve.
symptoms were bad stumble, loss of power almost like plugged cats or out of fuel, seemed to run a lot better at higher rpms, at 2500rpm would stumble bad and then 15 seconds later clear up and run smooth at 3500rpm then 25 seconds later drop to 2500 and stumble again.
under 1/2 throttle ran very poorly but seemed to clear up under full throttle, always wanted to die when coming to a stop, various cylinder misses detected but #2 was always an instant code set immediately after the engine was started. It has had a lean condition set occasionally on the rear bank but never the front bank.
weird sounds out the tailpipe at idle
Y-pipe where cats are having weird sounds and vibrating badly
hooked a vacuum gauge to the port for the power brake booster line. Here is what happened. At idle the gauge fluctuated rapidly between 10" and 5" of vacuum. When it was about to die vacuum readings dropped to between 0" and 5" of vacuum and again rapidly fluctuated till it either died or went back up to the 10" of vacuum and fluctuating really fast.
Everything about this driveability issue pointed towards an ignition problem or electronic issue.
I tore apart the motor yesterday and found this, a broken valve spring on the #2 exhaust valve. The valve could be unseated with my finger ... Hopefully this is the root cause of the problem
