Yes, a inductor sortof resists current changes, just like a capacitor resists voltage changes. In fact, inductors and capacitors are current/voltage mirrors of each other. The way I like to think of inductors in circuits is that they give inertia to current. They don't of course, but it seems a useful conceptualization technique.
In the schematic without the diode, if everything starts out at 0 and the switch is closed, the current will be a exponential decay toward Vs/R. Initially all the voltage is accross the inductor, and in the steady state there is 0 voltage accross it.
The interesting stuff happens when the switch is opened. At any one instance, the inductor will maintain its current constant. This includes the instance the switch is opened. Without the diode, there is no obvious path for the current. The inductor voltage will increase to whatever maintains the current thru it.
A mechanical switch works by touching together two conductors. When the switch opens, the conductors move away from each other. This can't happen instantly, so when the switch first tries to stop the current thru it, the contacts will be very close together. It won't take much voltage to cause arc over. Once the arc is started, the gas between the contacts becomes a plasma, which has high conductivity. The arc can therefore continue for a while as the contacts move farther apart. During this time, the voltage accross the switch isn't zero, so the inductor current decreases. As the contacts move further apart, the arc voltage increases, decreasing the inductor current more rapidly.
Eventually the current is low enough that it can't sustain the arc and the switch finally opens for real. At that point there is little energy left in the inductor. The only place for that current to go is onto the inevitable parasitic capacitance accross the inductor and other parts of the circuit. Every two conductors in the universe have some non-zero capacitance between them. This capacitance is small, and therefore the voltage will rise quickly. This also decreases the current in the inductor rapidly. Eventually a peak is reached where the voltage on the capacitance actually starts to push the inductor current the other way. In a perfect system, all the energy on the capacitance would be transferred to the inductor as current, but this time in the opposite direction. Then it would charge up the capacitance again in the opposite direction, and the whole cycle would repeat indefinitely. In the real world there is some loss, so each swing back and forth will be a little lower in amplitude as energy is lost as it is being sloshed back and forth between the inductor and the capacitance. Voltage plotted as a function of time (as a oscilloscope does) will show a sine wave with amplitude decaying exponentially towards Vs.
Capacitor selection involves a lot more engineering than just voltage and capacitance. Your plan could make the circuit worse instead of better.
High value ceramic caps are fragile, and have a dangerous failure mode in automotive applications: When they crack, they tend to become a low-value resistor. An automotive power system can supply high currents into this low resistance, dissipating enough power to start a fire. You can get special "automotive" capacitors, but inside they are just two capacitors (of twice the capacitance) in series, so that both have to fail before the fire starts. I expect you will find better cost and availability to just put two in series in your circuit.
High value ceramic caps are fragile. Some manufacturers only recommend placement with reflow, not with a iron that heats each end individually. Don't expect great reliability if you hand-solder the caps in there.
I would think high-temperature electrolytic capacitors should last the life of the vehicle. Replace, if you have to, with good-quality ones. But the designers of the ECU were designing it to last and you can assume they chose the capacitors wisely.
Best Answer
There are many ways to answer this question. I'm going to answer it one way, and you'll just have to keep in mind that you're not getting the whole story. Also, I'm over-simplifying it for the sake of discussion. Here goes.
Impedance is the "effective resistance at a given frequency". The impedance will be measured in ohms, and depending on the device the impedance will change depending on frequency.
Resistor: The "impedance" of the ideal resistor is the same regardless of frequency.
Capacitor: The impedance of the cap goes DOWN as the frequency goes UP.
Inductor: The impedance of the inductor goes UP as the frequency goes UP.
Now, imagine a normal voltage divider made from a couple of resistors. Because the resistor has a constant impedance over frequency it will divide down the voltage evenly for all frequencies.
If you replace the lower resistor with a cap (figure 3 from the web page previously linked to) then you have something different. This will reduce the amplitude of high frequencies more than low frequencies. Effectively making a "low pass filter", which lets the low frequencies pass through, but attenuates the high frequencies.
Now, if you put the cap on top, and the resistor on the bottom, you get a "high pass filter". This will allow the high frequencies to pass through, but block the low frequencies.
The high and low pass filters mentioned are variations of an "RC filter"-- a filter made up from resistors and caps. There are such things as "LC filters", with are made up from inductors and caps. Don't ask me why "L" stands for inductor, but it does. And I'm sure somewhere there is an LR filter that uses inductors and resistors.
The basic concepts of LC and LR filters are similar to the RC filters-- using the various impedance vs. frequency characteristics of the components to create the type of circuit that you want.
Inductors tend to be used instead of resistors in situations where the current of the "pass frequency" is high. But this isn't always the case.
I intentionally ignored one aspect of inductors and caps: They can both be used to store energy. That could be a lesson for a later time, since it can get rather complex.