engine light blinking - catalytic damaging misfire on 2003 Ford Taurus

MIL came on ,code was PO156 O2 sensor,bank 2 sensor 2,light goes off for few hundred miles, then comes on again for 75 +- miles,stays off few hundred miles.Driving expressway at 75 mph engine light starts blinking, engine begins rough operation,at idle engine very rough almost stalling.engine temp. normal.,after cooling I started car i noticed the # 3 cylinder intake pipe was very hot to the touch ,other intakes were cool, clicking sound from area of # 3 . I installed new wires plugs and coil. Could it be a broken valve spring of carbon blocking exhaust port ? Car has 230,000 miles, alway used synthetic oil.

by in Smyrna, GA on January 23, 2010
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2 answers
ANSWER by , January 24, 2010
The flashing engine light is from an engine misfire, you should have a P0303 code if it is cylinder #3 that is misfiring. With this kind of mileage, and the noise, you'll want to get a good idea as to the mechanical condition of the cylinder. Check the compression and perform a leak-down test if the compression is low.
ANSWER by , February 03, 2015
Driver, I'm curious as to what you found out. We just had the same problem and I'm trying to decide if we need to ditch the car ASAP or if its worth fixing. Thanks!