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Message: [QUOTE="JD3020, post: 661849, member: 373"] "New" engine in and has probably had an hour or 2 of run time, had a few hiccups at first since i had completely drained the fuel and oil rails, but is fine now. I've put maybe 40 miles on, but its spent a lot of time at hi-idle while i was doing a coolant flush. When it first starts up it runs extremely smooth, very little shake to it, sounds good, and no issues. After maybe 10 seconds or so, the idle begins to hunt. Normal idle is 700, but it'll go from 600 up to 800 when it gets really bad. Once it starts to warm up the idle goes back to normal, but it begins getting rougher and a slight knock. My old engine had a very rough idle, and had low/uneven compression, but this isn't that bad. The "new" engine is a 97 with 120k miles, bottom end looked about new, I added a Melling LPOP, welded and opened up the pick-up tube, and re-sealed everything. The mechanical fuel pump only has about 1500 miles on it, although i haven't checked fuel pressure yet. I did re-use the same electronics/sensors from my old engine. I've got another cam sensor to throw in as it did throw a CPS code the other day, and i've got a couple used IPR's, as well as a new one somewhere to throw in. It'll pass a buzz and CCT test all day long, ICP and DC% look good, and nothing looks out of the ordinary. Going down the road the truck runs smooth, no smoke, although it does seem a little down on power, but hard to tell. So what in the hell is causing this? [/QUOTE]