Thread: 98 gtp missing...p0300

First off ive never done the forum thing before and i know there are a ton of posts about this, but none really have a solution to my problem.

I have a 98 GTP with 169,xxx. Lastnight it started missing when boosted, so i ran seafoam trough the tank and the middle vac line on top of the sc. I drove it home and let it sit over night.

Today i started it and it was missing at idle, and backfiring pretty bad. So i changed plugs(ngkTR6's) and wires(napa golds) and that didnt stop the problem so we tested the coil packs and when cyliner 6 and i think 3 were unplugged the backfiring stopped even under a load, so i replaced the top 2 coil packs and am still having the same miss. The only code it is throwing is p0300.

Ive been reading the common causes of the p0300 code are cat or egr issues. But i have both deleted. Any tips? How would i know if it is a CPS?

Wow. sorry didnt realize there were that many. Im going to try moving an injector in the morning even though i seafoamed. How much do those usually run? and what # do i need if that does turn out to be the problem?

well i the guy i bought the car from bought it modded and he didnt know much. but..3.4", SLP headers/exhaust, 180tstat, has to have pcm because shift points are raised, k&n intake..so TR6's should be fine. also me and a buddy took the oil fill car off the valve cover and looked at the visible rocker and it is sort of a shiny polished red. so possibly 1.9rr's and 90# springs?

how would i figure that out?