Ok so my car has been dumping gas lately to the tune of about 250 miles to the tank, just awful. So I take out the spark plugs to find out that the number 5 and 4 plugs arecompletely broken. Those little metal conductors on top of the plug were completely missing, like they have been melted off. So my question to you is this. What could have caused this? I checked with a scan tool what my computer thinks the collant temp is and that is just right, 200 deg. The oxygen sensor at idle reads lean rich, lean rich, lean rich over and over. The timing is at 20 deg. There is no engine knock. The only thing I have noticed strange is that when i press the gas while driving, the car doesnt downshift as readily as it used to. Also I keep getting a code using the snap on scan tool, it says 257, boost control failure, overboost. I don't know what this code means and no book claims that code is an overboost. The thing I did do to try and fix that is replace the new boost control solenoid I had in the car with the original. I haven't driven it since then but I will be monitoring the spark plugs alot now. Anyone who can help me with this problem, please help thank you!

Well don't use platinums for sure, but if you're getting too much boost, you could be running lean, and eating them up.

Detonation may be happening, and you probably have some knock. 20 degrees is a lot with 0 knock....

That'* timing ADVANCE, right? I'm not sure what it should be at idle specifically with our cars, but it sounds right.

well my scantool would say +20 or -20, + meaning advance, or -20 meaning retard. When I got my car the fuel filter was on backwards and I would get SES and it saying it was running lean. Maybe your filter is clogged up