I've been trying to figure out lately what is causing my truck to idle rougher than it used to. It's like there is a miss or something....When I first do a cold start after it has sat all night it will idle a little rough for about the first 5 minutes & there is actually a rocking motion in the truck back and forth that you can feel when you're sitting in the cab.....you can see the tach bump up & down slightly....What could cause that.....I just adjusted the valves a couple of weeks ago.....No codes at all & it cranks right up with no hard starts....

Only other thing I was wondering about is I've noticed that sometimes the grid heaters don't cycle some lately at night when I've thought that the temp was low enough that they would.....Is it possible that the problem could be caused by a bad IAT sensor....I've only noticed the rough idle lately now that the weather has warmed up.....

 

Did you recheck valve adjust? Cold. Possible valve too tight or injector leaking. Pull injectors and have them tested.

 

i did some transmission work on it recently & now i'm starting to wonder if the two are related....

i did a really dumb thing....i put a new PML pan in & then didn't check my fluid level closely enough....I wound up running the truck for several days about 3 quarts low on transmission fluid.....I never saw the transmission temperature reading get up past 175F but I saw some vapor/smoke coming off the dipstick tube when I checked it a couple of days ago.....I immediately put a quart & then more later when I noticed it but I'm starting to wonder if I did any damage was done & something might have gotten warped....

Would this cause a weird problem on cold start where you can feel kind of a rocking motion in the truck while it idles......like something is out of balance.....could it be torque converter or something like that?

 

I have seen torque converter out of balance cause vibration, usually smoothes out when you increase RPM and does not go away as engine warms up. If engine runs good with no black smoke at start up it could be converter.

 

thanks....ever heard of an issue where running too high or too low on fluid could cause torque converter to get out of balance.....From what I've read I think it starts to fill up when you place it in gear.....I was thinking that all the fluid would drain back down into the pan while the truck sits at night....I was wondering if the fluid wasn't distributed in it evenly it might shake some.....That might explain why the truck only does it after it has sat for hours overnight.....

 

There is a valve in trans cooler line called a drain back valve and it purpose is to prevent trans fluid from draining from torque converter.