idle problems for over a year - please help
 

Hello all, I have an early '99 that I bought at a county auction and have had trouble with it having a rough idle and miss when warmed up to operating temp and will stumble with idle until it finally dies but sound great when cold. I have put on new IDM, IPR, IPC, injector O-rings, fuel pump, fuel bowl rebuild, fuel pressure rebuild, batteries, 2 CPS's, exhaust back pressure sensor and cleaned back pressure sensor tube, and glow plugs. I bought a AE and can not find anything with it. The only 2 big things that I can find on that might point to something is that the idle smooths out and the miss goes away when partially opening the fuel drain valve and everytime I try to do a cylinder contribution test, the engine dies emediately. the rough idle that I speak of is the sound of the miss, the truck vibrating, and the rpm's going from 500 to 900 and sounding like it almost dies everytime it slows to 500 and after a while actually does die. Also, if you rev the engine with the pedal, it seems slow to react, revs up and dies when returning back to lower rpm. Any ideas? Anyone? Thanks for reading.

Same thing happening with my truck. Replaced the idm and PCM, problem is still there. Ifi get it figured out I'll let you know.

Thanks Tyrexs. I remember reading somewhere that the idle smoothing out when opening the fuel drain was a sure sign of bad injectors, but I can not find it again to verify.

check you hpop psi hot

OK, there is another problem. I have seen what psi the high pressure oil system should have at different rpm's, but not for early 99. I know that the early 99 has a smaller HPOP and will run lower psi but not exact numbers. At warm idle, it jumps around between 660ish and 740ish. I have just replaced injector O-rings with no change in rough idle.

I can`t believe no one has mentioned injector wire harness, common problem one side can be bad or only part of the harness is bad. but the symptoms you described definetly sounds like harness issue to me

Matthew-thanks for the idea but not the harness - checked that already

ToMang - I forgot to mention ealier that I already installed new IDM - my AE is on it's way back from Dallas. should have it here tomorrow to check % IPR and give you exact numbers. I know I checked it before and numbers looked OK. I ordered a fuel pressure gauge and should be here Tuesday but I am pretty sure that pressure is okay because I have kept the same problem through 2 different fuel pumps and 2 different fuel pressure regulators and I have checked fuel return line and it is not clogged. My neighbor found me 2 articles saying that injectors scratched on the inside by water can cause this exact problem. They say that the scratching on the inside makes it more difficult for the hight pressure oil system to push the fuel through so when it is at idle (with lower high pressure oil pressure) and high fuel pressure also working against the injector pushing out the fuel, it will missfire. This makes sense because the miss goes away when either lowering fuel pressure or reving the engine (making a higher high oil pressure system pressure). I think he has found my problem. I already emailed Rosewood Diesel to see if they can rebuild them for me. Thank you all for your help!