Unexplained resistance/braking sensation

Howdy, I'm curious to see if anyone has any theories to an unexplained problem I've recently had.

It's a 2010 with 191k miles. I've had it a little over a year and never had any problems with it. I'm on a road trip and currently about 2000 miles into it. It's performed with no problems until now. Consistently reported around 48mpg at every fill up (which is along the lines of what I normally expect with this car).

Recently, the mpg dropped from 48mpg to 36mpg. At the same time I noticed that I was having to apply a lot more throttle to keep the car up to speed than normal. If I took my foot off the gas, instead of coasting like you would expect, you could feel the inertia kind of shift back and the car would start decelerating faster than would normally happen. It basically felt like there was a mini-parachute pulling me back at all times. It was very apparent that the engine was working way harder than it should have to.

This behavior happened for about 200 miles, before it suddenly stopped for about 30 miles, then started up again for another 40 miles, before disappearing and the car has been operating normally for the last 100 or so miles.

When it was happening, I pulled over to check the tires (they were fine) and I fully engaged the parking brake and disengaged it to see if it had somehow gotten stuck (it had no effect on the performance).

I took it to a Toyota dealership. They said there was no evidence of a problem with the braking system. Pads looked fine and no sign of uneven wear. Calipers were releasing. Rotors ok. Parking brake was functioning and adjusted properly. No engine codes were thrown. So they couldn't diagnose it because it wasn't currently happening anymore.

So I'm kind of stumped at this point. My only theory would be that somehow the regenerative braking system had engaged itself and was stuck on. I don't know if that is even possible though, my guess is they would have engineered a failsafe for that.

I'd be curious to see if anyone has experienced something like this before or has an idea what was happening. Thanks.

 

Thanks for getting back to me, sorry I'm on the road with limited internet. It's definitely not in B mode. I've been in Colorado going through the mountains and have been switching between B and D mode a lot so I'm always aware of what mode I'm in. This issue occurred when I was in Kansas, on super flat consistent highway and I'm very certain that I was in regular D mode. The issue also "fixed" itself when I was on the highway and wasn't touching the shifter. Thanks for the idea though.

 

Thanks for the ideas, sorry I'm on the road and don't always have access to internet. I've been thinking about the EGR system, although I haven't heard of this type of issue being caused by the EGR. I talked to the dealership people and they seemed to think that it couldn't be an EGR issue without throwing a code. I don't know if that's true.

No recent tire replacement, and no brake work. This occurred about 2000 miles into a roadtrip and the car had been performing beautifully up to that point.

I'll do more research on brake drag, although I have been checking the heat of the rotors periodically and nothing seems off. I would suspect that a brake problem would throw heat, especially after long distance at 70+ mph. I'm on the road so I don't know when I'll get a chance to jack it up and try spinning the tires.

It was behaving well again the last 500 miles(ish) but it seems like the issue just showed up again. It does actually feel like you're trying to drive in B mode (but 100% it's not in B mode). You just constantly have to be pushing the engine much harder than normal to keep speed up. Like the transmission isn't geared right and you constantly have to keep the rpms high. Nothing prompted the change, it just happened. At slow speed it isn't terribly obvious. I put it in EV mode in a parking lot and it drove under EV power alone, so I don't know if that eliminates any possibilities.

I'll see how long it goes on for this time.

 

Thanks, I actually did consider this when I was trying to convince myself that I was just imaging things. Unfortunately that wasn't it. You can actually feel the difference in the way the car drives and the engine is constantly running harder. The mpg drop was huge (48mpg to 36mpg). When the issue fixed itself I could tell immediately just by how the car drove and the engine felt. This was heading west in Colorado towards Denver, so basically the same highway conditions as Kansas.