Hey bought this 2003 duramax off a guy took it for a test drive and ran awesome everything good, make the deal he takes off and i go and park truck. go to start it again and it would not fire. I message the guy he says quick shot of ether and it starts so I looked into it a bit and figured maybe there was a fuel problem so started by changing fuel filter and still no fire I could prime the crap out of it and go try and crank and then come back and the primer was soft again. So had to atleast get it started so gave it quick shot of wd-40 and fired right up and noticed at idle it would surge on and off and at times not do it. take it down the road and floor it and has normal power but yet shut it off and then instantly crank key again and would not fire.. Any Idea or suggestions Appreciated thanks!!