Blinking CEL on Downshift
 

'03 Civic EX, 210k miles, owner for one year.

Getting codes:
P1259 VTEC System Malfunction

P0300 Random/Multiple Cylinder Misfire Detected
P0301 Cylinder 1 Misfire Detected
P0302 Cylinder 2 Misfire Detected
P0303 Cylinder 3 Misfire Detected
P0304 Cylinder 4 Misfire Detected

Basically whenever I am driving down a slight hill, sometimes on a flat surface, and just maintaining speed the CEL will flash. The car doesn't actually seem to drive any different while it is flashing, and it stops flashing if I slow down a lot, or sometimes stops quickly on its own. I can prevent it by shifting into neutral, or by accelerating more, but neither seems like the best long-term solution to me.

I've gone through probable causes of the P1259 code and replaced the VTEC pressure switch, cleaned the VTEC solenoid valve screen, changed the oil, and done one drain/fill of ATF, but the problem persists.

Halp?

Re: Blinking CEL on Downshift
 

Erase codes, see which misfire code comes back.
Your driving condition description sounds like it may have clogged EGR ports in the distribution plate.

VTEC code, need more info like how it repeats, oil pressure when the system activates, does the solenoid actually work, does the PCM operate the solenoid, does the PCM receive the signal from the pressure switch, and did someone pull the cylinder head off and apart and lose the oil passage plug from the valvetrain?