When Engine Vibration Becomes Noticeable (Toyota iQ DBA-KGJ10)

When idling at a stop with the transmission in D (Drive) position, the engine vibration transmits throughout the entire vehicle body and is very uncomfortable. I noticed that shifting to N (Neutral) somewhat reduces the vibration, but having to shift from D to N every time I stop at a traffic light is cumbersome and stressful.

This was the complaint when I first received the vehicle, which was already about a year ago.

2009 model DBA-KGJ10 1KR-FE CVT Mileage 66,000km

This symptom is caused by deterioration of the vibration-isolating rubber called engine mount insulator, which connects the engine (+ transmission) to the body. The engine creates powerful vibrations as it rapidly moves pistons back and forth while burning fuel, but passengers hardly feel these vibrations because of the excellent cushioning material called engine mounts.

As a side note, in motorsports, the distortion of these engine mounts interferes with power transmission response, so it’s common to replace them with harder materials. This aims for a slight improvement in power transmission even at the complete sacrifice of comfort. With this modification, engine vibrations transmit throughout the entire vehicle body, creating such intense noise that even conversation with a passenger becomes difficult.

Now, vehicles generally have three mounts (some models have an additional auxiliary one), and in the case of FF vehicles with transverse engines like the iQ, the uncomfortable vibration is largely caused by deterioration of the engine-side mount (on the driver’s side in the case of the iQ). The engine + transmission mass has its center of gravity on the engine side, which I believe affects the characteristic shape of the mount and weight distribution.

(Left) New, (Right) Original installed part

You can see how the rubber has deformed under the engine’s weight, and the gap in the red circled area has increased. Deterioration in vibration absorption capacity or interference where parts shouldn’t touch causes vibration.

This engine mount has a vacuum hose connected to it.

The vacuum hose connects to the engine’s intake manifold and uses the resulting negative pressure (vacuum) to control the engine’s vibration characteristics. In other words, it has a mechanism that changes hardness between normal state and engine load state, and by sensing the engine’s negative pressure through the vacuum hose, it changes the mount’s characteristics at appropriate times.

It has a somewhat elaborate function: it softens to absorb vibration during idling and hardens during driving to suppress engine movement.

Ideally, all three mounts should be replaced, but for the purpose of reducing uncomfortable vibration, replacing the main mount on the driver’s side is often sufficient, and this time we initially kept costs down with just this measure. I feel it reduced vibrations by about 80%.

However, once you’ve experienced uncomfortable vibration, even the remaining 20% can become stressful. After about a year and 6,000 km, the complaint was that noticeable vibrations seemed to be increasing again, so the vehicle returned to the shop.

These are the remaining two engine mounts that had not been replaced.

When force is applied, there is indeed deterioration and cracking, but they haven’t reached the point of rupture. Even in the worst case where they rupture, the engine won’t fall in a dangerous manner due to the structure, so using them until complete rupture as in the following example isn’t a bad maintenance schedule.

What Happens When Engine Mounts Are Used for Over 300,000 km? (Toyota Vitz UA-SCP10)

However, this slight deterioration is certainly causing the vibration stress experienced during daily use. All three mounts were refreshed, improving both vibration and drive response.

Please enjoy your comfortable car life.