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Rough Idle?

39K views 14 replies 7 participants last post by  nhwrench 
#1 ·
My truck seems to be idling a little rougher than it has in the past. It's a daily driver, some smoke on start-up and just a little when run past 2400 rpm. I use Power Service or Seafoam in every other tank, so I'm not thinking the injectors are dirty, but I guess they could be. I had a new injector pump put on a while back, could this have anything to do with it? It has idled just a little rougher since then, took it back to Ford and they said nothing was wrong. I've lived with it a while but now it seems to be getting worse.

Truck just rolled 100k a couple months ago. Any thoughts?
 
#3 ·
Thanks Drinky!

Sorry if this gets wordy, just trying to describe what is going on as best I can. I'm a college student who loves his truck, but I'm certainly no mechanic.

When I'm on the pedal everything is smooth, but at idle the whole truck shakes. The truck seems to run ok and I've only felt like it would stall a couple of times. Just gave it some pedal and back to normal. The truck shakes at idle, I can look over and see the top of the passenger seat vibrating back and forth. Sometimes when starting off from a red light or a stop sign, I'll give it pedal and it seems to hesitate for a second or two before it kicks in and the tach goes up. I usually get a puff of white smoke at start-up and just a little bit of constant smoke at idle.

My first thoughts were dirty injectors and an improperly installed/adjusted injector pump? That's all I've got.
 
#4 ·
Could be a timing issue, did you have it properly timed when you had the new IP installed? If it was installed by the dealership chances are they just lined the timing marks up and called it good. If this is so then your timing is more than likely retarded. How about your return lines? If there are any leaks in your return lines? Check to see if any of them are wet anywhere. Leaky return lines will cause these symptoms. Are you still on the original injectors? If you have a new pump supplying old injectors it can cause the old injectors to not perform well. As a general rule it's a good idea to replace the pump and injectors at the same time.
 
#6 ·
If it was installed by the dealership chances are they just lined the timing marks up and called it good.
Had it done at a dealer, a fairly shady one at that. What kind of a shop can work on injector pumps? Is it something I could try to tackle myself?

I don't believe the injectors have ever been replaced. How expensive a job is this? Who is qualified to do it?
 
#5 ·
It could just be air intrusion. Different amounts of air intrusion have different effects. a little bit will cause a stumble. A lot will cause RPMs to run up right before it dies. When my pickup foot was failing I could get on it and it would run, but then if I let it idle it would die.

a clogged return will cause timing to advance, which also causes poor performance, but it doesn't sound (haha) like that is the problem so far.
 
#9 ·
I'd try a Navistar shop first, a lot of them have old-timers who've worked on these things a lot. After that try to find a municipal or U-Haul mechanic, they tended to see a lot of these in vans, dump trucks, or school buses as well.
 
#11 ·
You may have noticied that I have been trying to resolve the very same issue with my truck. I have replaced the IP, injectors, return line caps and o rings, and even done a valve job. I had low compression on one cylinder due to a worn valve guide. The only thing I haven't done is having it timed properly. If you find a solution, please post it and I'll do the same.

I notice the rough idle more so when it hot, is this the case with yours?
 
#12 ·
I just bought a 94 F-250 that had a real bad vibration/ shake at idle that would smooth out as you gave it fuel. took awhile to figure it out. It turned out to be the fan clutch was shot and causing the whole motor to shake at an idle. Just somthing else to consider.
 
#15 ·
rough idle, hard start

this could help lots of idi owners, .
I did the injector cap replacement , filter head check. mechanical lift pump to electric pump thing.
I still had a long crank and rough idle.
the bed was off (replacement due to rust , in the n.east) when it was running, I pulled the vent on the front tank to see air bubbles in the return line bubbling in the fuel.a great tool for fixing this problem...I found the shrader valve was leaking . fixed it but no gain in starting. then I heard a hissing sound from the lines about 1' from the tank.
the plastic lines go from plastic to steel then plastic... the steel had rusted and was letting air in.!!!!!
I cut them out , installed rubber lines and clamps over the plastic lines with 1" or so off steel lines in them, clamps and it starts and idles great !!!!!
hope this helps everyone. please repost this everywhere !!!
dave.. aka: nhwrench.
 
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