driving home the other day the van quit, it was snowing and acted like it like the engine got wet,the engined turned over very hard like a weak starter and backfired some, it would run but not very well, knocking and backfiring, check out battery ,ok, check out starter,ok, now it won,t start at all and turns over very hard,reads PO300 code,i put in new head and intake gaskets, new oem plugs about 3 month ago.it has 140000 miles and has always ran great .engine is a 3.4 any ideas out there ,, thanks skip