Cyl 4 Misfire (Code P0304) 2.0 Liter. Stumped!

[bobinyelm]

Just purchased '96 4 cyl Contour for my daughter. Extremely nice car for mileage (137K), but "Check Engine" light is on.

I ran a scanner check and got P0304, Cyl 4 Misfire.

Pulled plugs and regapped to 0.050" (they were at 0.070") and replaced plugs (swapped #1 and #4 plugs). and reset light. Car ran smoother and previous slight hesitation was gone. Thought problem was solved.

10 miles later, light is on again.

Obtained maintenance records for car and found that the "Cyl 4 Misfire" has been a problem for past 40,000 mi. Owner replaced wires, plugs, etc.

I plan to swap #1 and #4 Fuel Injector (in case #4 is too lean) to see if problem moves to %1 Cyl.

Also plan to look for intake leaks around intake manifold near #4, though plug didn't look like it was running lean.

Any other ideas out there?

Thanks,
Bob

[beyondloadedSE]

you may want to add some electrical grease to the spark plug so you know it has a good connection with the wire.

[bobinyelm]

The problem has now morphed-

The Cyl 4 Misfire has stopped coding, and now I am getting a
PO401 and P0420, which are:

1st Bank Cat Efficiency (I assume this is the downstream O2 Sensor)
and
EGR Flow Insufficient

Can/should the EGR valve be cleaned (and is it worth it) or should it just be replaced?

[beyondloadedSE]

Thread on contour.org discussing this problem