2006 F250 6.0 King Ranch - Just bought a month ago w/150K miles.
At freeways speed, around 1500 rpm, I get a shake or shimmy until I can get a few more RPMs. It only does this when I am maintaining speed (55-60ish) or going on a slight incline and I am accelerating SLIGHTLY. Today I was trying to pinpoint when and what was going on, I noticed that the RPM gauge would sit on 1500 as it shook and occasionally jump up smoothly a few RPMs and then back down to 1500. Other than that, it runs great. For the life of me, I cannot figure out what is wrong. No codes. I've thought about stiction, but does this no matter how warm it is. I've also thought about a sticky accelerator or a bad FICM. Can someone give me some ideas?

Background - performed EGR delete about 3 weeks ago and broke 2 injector connectors. Over the last 3 weeks, I've replaced all the injectors AND the wiring harness. Had noticeable miss for 2 weeks because wire broke in harness that I didn't find out about until after replacing injectors.

 

Do you have a way to Monitor via scan gauge ? take a look at VGT, may want to clean up Map, Iat2, Ebp

 

I have an SCT 7015, which has a number of active scan gauges, but I'm ignorant as to what I should be looking for. Took a good look at turbo when I had it off for EGR delete and it looked good. I have good turbo power when I step on it, but problem is happening when very little pressure is put on accelerator.

 

Monitor EBP,MAP,VGT, BARO and post Values for koeo cold soak, low and HIGH at 2500 rpm all these will be in park , no hvac radio power on.the IAT2 senser will be sooted if you haven't cleaned it in a while.

 

After eliminateing a engine issue you may need to look at your tires and drive shaft.
All four tires in balance; equaly inflated; equal wear; bump or bulge in the tread; steel belt turnng.
Drive shaft damage; shaft in balance; u-joint play etc.

 

X2 on driveline issues.

 

I just had my front end redone Moog ball joints tie rod ends, had a bounce going on, the tech said that the tires should be rebalanced Every 6 months for Tire ware. that would Definitely do it. all though the Turbo sticking would too. let's rule out some things

 

My 05 has done this since it was new. I did a big search about it back then and found others having the same issue and nobody knew what to do or what causes it. I just hit tow/haul mode when it happens to get RPMs up and it goes away immediately. My best guess is that it's from asking too much of a motor at low RPMs, and I have the tallest rear end. Not sure if my Torqshift may be partially to blame for not downshifting when it should.

Just my 2 cents, which may be worth far less than that.

 

1500 is not low RPMs. To the OP, what gear are you in at the 1500, or is it at different speeds and different gear, always at 1500 rpm? I have a bit of trouble with my tires holding a large amount of small rock, until I hit a decent speed and spin some out, the off balance wheels will give me this issue but it's at several wheel speeds not one RPM of the engine in any gear.

 

Is the transmission fluid fresh? Sounds like you might be describing torque converter shudder.