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Discussion Starter · #1 ·
Hello Cummins guys! I’ve been having trouble with my 97 12 valve Idling. On a warm summer day, It idles at about 800 Rpm in P and N, it drops to about 750 when in D. If I drive it hard on the highway for a few minutes, especially if I hammer on the throttle a few times getting on the highway or passing, when I get off the highway and stop at a light it idles at 300 RPM or sometimes even lower and barely stays running. When I hit the throttle it idles up and runs fine, at least it seems to run fine. Sometimes it’ll stay idling like that for days even if it sits over night I’ll start it and it’ll idle very low even in P and N. I have a fuel pressure gauge and it doesn’t drop ever, my lift pump seems fine. I don’t know what to do. In the winter the thing never idles right lol but then again it’s always cold as hell here. Thank you!
 

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Discussion Starter · #3 ·
I did look through there and didn’t see anything with this exact problem. When it runs hard it drops rpm like that. When it’s just sitting in my yard idling while up to temp it’s at 800 RPM or so, but it drops to like 200-300 rpm after dragging a loaded trailer onto the highway with the pedal smashed through the floor like the Flintstone-mobile. I was told it was governor springs being too tight or too loose, the torque converter could be locking up, or a million other things.
 

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Have you inspected the linkage? The stop is a bolt with a locknut. It could be worn or the piece that rests on it could be worn. What is the idle speed while in gear, AC on, engine at operating rpm?
 

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Discussion Starter · #5 ·
The linkage is all fine. Idle speed in gear, AC, all warmed up at 750 rpm. I’ve had it at 800 rpm and I’ve had it at 700 rpm. 750 feels perfect, if it’s at 800 it just wants to pull too much at stop lights on its own.
 

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This could be a lot of different issues. I would check your basics first. These motors run on basically 2 things, Fuel and Air. If you say you have checked your fuel then start to check for air leaks. You could have a leaking boot or something. Only way to really tell if you have a leaking boot is to take your ends off the turbo out let and the inlet on the motor and seal them off then pressurize them to about 40PSI and then hold it for a while and see if the PSI drops. But thats where i would be looking next.
 

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Discussion Starter · #7 ·
I actually had a serious air leak about a year ago. Fixed that and threw a new turbo on it, same time I check for boost leaks in the system. It held pressure well. I don’t think it’s air.
 

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Have you checked your injector seals. Could be leaking air at the cylinder then
 

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Just because you did them does not mean they all went in correctly and are not leaking. More times then not the things you mess with are the things that are causing your issues.
 

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Im just giving you some trouble shoot procedures. If you think they are good then leave them. As I dont know your mechanical ability I cant say much after that. Do you get any white smoke during start up? dose it black smoke a little bit when you take off hard from a stop?
 

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Discussion Starter · #13 ·
I understand, it shoots black smoke no matter what, if I’m very gentle on the throttle it’s under control, but typically shoots black smoke a decent amount. I’ve done all kinds of adjusting of the AFC and fuel plate yet it still smokes a lot.
 

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Thats a very good indication of not enough air in the cylinders. Can your read how much boost pressure you have?
 

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hmmmm. interesting. have you messed with the timing of the Injection pump?
 

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Lets go back to the dragging tq converter theory. If it is 4WD have you shifted the transfer case to neutral when the engine RPM drops so low? If it is a fuel or air issue it would misbehave every time you go to idle.
 

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Yeah, The being speratic kinda just threw me off. I never really hurd of a dragging TC normally they just dont work lol
 

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Discussion Starter · #20 ·
I have not put the T-Case into neutral while it happened, I didn’t think it would change much versus putting the trans in neutral. Yes it is very speratic though.
 
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