I was towing a Uhaul trailer last weekend and when I would get to 6th going 70mph at about 2500RPM, I'd start getting the RPM tach bouncing about 5-750 RPMs and the truck noticeably rocking. This should 100% not be happening. Does anyone have any experience with this?
Took it to the dealer and they found a crankcase PCV sensor code (P051D + B) and they're ordering the new sensor but shipping means it won't be here til Tuesday but said nothing else was wrong.
Are all of these people just ODBII jockeys? Why isn't anyone finding something?
Finally got some time to sit down and decided to re-read your post. I noticed you mentioned the tach was pretty active when your symptoms occurred. When was the last time you pulled and inspected your throttle body?
The PCV issue would normally only occur under load and be less noticeable in higher gears/speeds. A defective PCV can stifle the vacuum air and cause misfires under load which is most obvious right before your vehicle would normally downshift, and is easiest to duplicate in the lower gears. This does not sound like your issue based on the description you gave.
Did the truck seem like it was bogging down? Did it have the "rumble strip effect"? Any surging/lunging?
If you have Forscan you can pull your desired vs. actual degrees for the throttle body and see if they are close (usually within .01).
You could do a smoke test to check for vacuum leaks (the symptoms make a strong case for this), and see if you have a big leak somewhere. Would likely be significant to cause that much movement in the tach in high gear. You can make a smoker pretty easily and run the test yourself to save the $100+ at the shop.
I'd be curious to know how you make out.
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