I just got this P0300 code 2 days ago(the first time was 3 months ago and they said I needed new plugs so I got it done and CEL disapeared until 3 days ago). Today on a cold start she runs OK for 2-3 minutes and then wham! it runs like crap. 3 days ago it started running very bad while I was 50 miles from home. 3 months ago it started being a little hesitant of the line on a gentle accelerate and when it got over 1000rpm would kick in better. I had plugs and EGR changed recently. The only time it does run proper(tried it today) is when I hammer it to the floor and it runs like it always did-fast and hard! otherwise its barely alive and dies once in a while. Is it possible I have valve spring issue? It's got 168,000km(105K miles) on 5.7L Hemi. ANY IDEAS GUYS? feel free to ask any questions thanks!