2016 Honda Civic: The Dithering Throttle
by Dan Edmunds, Director of Vehicle Testing on December 28, 2016
I just returned from a 2,000-mile journey to Oregon in our 2016 Honda Civic. It was an illuminating trip, but I didn't come away as enthusiastic about the Civic as I had been going in.
One of its more surprising and annoying traits became apparent during four long days behind the wheel.
The route to Oregon and back includes plenty of mountain passes and sinuous roads, but a surprising percentage of the distance — some 50 percent, I'd reckon — is straight and flat. Much of this mileage occurs on Interstate 5 and Highway 99 as they traverse California's great central valley.
It was on Highway 99 where I first noticed a gentle oscillating fore-aft tug, not unlike the feeling you sometimes get when towing a trailer. This gentle surge cycled at a rate of around two times per second, and it could last for miles on end if the road was farm-country flat and I held the throttle steady by using cruise control or merely locking my ankle in place. Either way, the surge was readily visible on the tachometer as a 50-rpm dither.
My wife even noticed it in the passenger seat. "What are you doing?" was how she put it. You know it's bad if it causes someone to look up from her phone.
Here's what it looks like:
This is not a particularly long-lasting example. Multiply this by 10, 20, 50 times, if you like. And the feeling itself is subtler than the jagged movement you see on the tach needle.
There wasn't one particular speed or rpm either. It happened at 55 mph, 63 mph, 73 mph — any number of typical freeway speeds on stretches of road that were flat enough to require no change in throttle input for a length of time.
I even noticed it at 35 mph as we cruised through a small town, and at that low speed the diminished background noise allowed us to hear a matching turbo-whistle oscillation. Imagine that sound cycling up and down to the tempo of the tach-needle pulsation for two or three minutes straight. Charming.
When doesn't it happen? Anytime there's a corner, a slight rise or dip, a change in traffic speed or a long hill to climb. The road has to be very flat and level, with no traffic influences on speed whatsoever.
I suspect this can only be happening because this car has a continuously variable transmission, a setup that can alter speed by either changing the throttle opening or subtly altering the gear ratio. It feels like some kind of ongoing steady-state calibration argument between the engine and transmission, with each trying to control the situation.
In my mind I'm picturing two outfielders trying to catch the same pop fly. Or maybe neither one can clearly see it and each is yelling, "You take it!"
On the other hand, this might not be a mere calibration weakness. It could signal the leading edge of a bigger problem. We're going to take it in and have it checked out to see if they can tell us what's going on.
Dan Edmunds, Director of Vehicle Testing @ 15,201 miles