Pulsation when "half-coasting" on Cruise

New-to-me 2010 Prius III, first time P= owner.

I'm wondering if this is a normal thing, or something I should have checked...and if it's something anyone else has experienced.

On Cruise Control at highway speeds, when "sort of" coasting, I get a pulsation reminiscent of the feeling when your ABS would engage while braking hard (obviously without the hard deceleration)...that grab-and-let-go, grab-and-let-go feeling at about half-second intervals.

This is while it's doing what I will call "sort-of" coasting, meaning (to me) where your MPG "gauge" is in the 75mpg-ish range, so not maxed out. Like you're on a very slight decline. ONLY happens (so far that I've noticed) at highway speeds. Does NOT happen (that I've noticed) when it's right at the 50-mark, or maxed-out at the 100-mark.

Is this normal? If not, should I be concerned? I find myself being hyper-aware of "unusual things" since I've never owned a vehicle of this type before...and I've only owned it for a couple of days.

 

I'll give that a look/thought.

I would have thought this symptom would show up under load/etc...or if not, that I wouldn't "feel" it in the drive-train (where I could feel it effect the way the vehicle rolls).

To clarify, I can feel the vehicle sort of "jerk" rolling down the road (down the rather long slight inclines, of which there are a lot where I commute to/from) again, as tho the brake (in a normal car) were being tapped at half-second intervals.

My thought is...this is something to do with P='s brain. Like P=s brain is saying "should I push this energy into the battery or not?" since it happens only when the car is "sort of" coasting (when the MPG gauge is somewhere around 3/4 of the max line)...and goes away if it goes all the way up (or back down to the half-way point).

BTW, I've decided on a name for the new (to me) Prius...The wife has gotten us into the habit of naming our vehicles. For instance my last vehicle's name was Irene Cara(van). Care to guess what it was?

Anyway, this one will be my Toy(Yoda)

 

Update on this symptom, which hasn't changed significantly since I initially reported it in October.

Shortly after the initial message(s), I got my hands on a little bluetooth OBDII reader & use TorquePro continuously for anything but very short trips.

Anyway, one of the "Gauges" I use is the RPM's.

I note that the symptom happens at any speed from 20 all the way up to highway cruising speed...but ALWAYS at the same RPM's. That RPM range being 1500-1600rpm.

Just so happens that RPM range is pretty much exactly the RPM range needed to keep the speed constant on a level surface, which is annoying

 

no perceptible kick...and yeah, reproducible off cruise

 

Never been in a normal vehicle that "lugged" in the manner you're describing.

I have, however, been in an 18-wheeler when the "engine brake" got engaged...and the sensation is eerily similar (except for the lack of deceleration). And if you've been in one, THAT is the sensation I'm describing.

I know the concepts are likely not even close to being similar, but that's what it feels like. Like the whole vehicle is shuddering at half-second intervals.

 

I noted the mechanic mentions (toward the beginning of the video) the vehicle came in with a noticeable "shudder". I'm wondering if my symptom is what he's referring to.

 

If it does end up being that tranny, looks like I can source a replacement pretty damn cheap. What should I expect from a local shop for installation? I hope not as much as your average tranny-swap, since it looks considerably easier from other videos.

 

a "fry" of that nature is electrical...got enough e background to recognize short-scorch.

someone in one of the threads mentiond thats why it's important to go with Toyota fluid, others will eat the insulation...leading to exactly this result

 

An interesting wrinkle I should have noticed a LONG time ago but...

The symptom doesn't happen with a cold engine/tranny, even if I "let it warm up" first (I don't pull out of the driveway til Coolant Temp is over 100 degrees).

For the first 5 minutes or so of a drive, it's smooth as silk at any RPM. Then it's like a switch gets thrown, it doesn't "come on gradually"

Does that mean anything to anyone?

 

Not sure how or what I'd monitor to find that out. Any pointers?

...again, using a bluetooth gizmo & TorquePro with (theoretically) the most recent list of PIDs I found somewhere on Priuschat (can't remember where)

 

I've got a 40mile commute home from work in a bit over half an hour, so this is the perfect time to give me something to watch (or watch for)

 

Can anyone with more experience with TorquePro weigh in with which PID Leadfood is talking about? I've been all the way through the list & don't see one like the one(s) described at the beginning of his post .

Service 01 PID 03