If the throttle signal is fed through a 4.7K resistor with a 100Uf cap to TPS ground, the effect is to smooth the TPS signal which is equivalent to holding your foot real steady. The new plug in boards allow making the modification on the plug in rather than to the car harness. An etch cut is made to the TPS signal line between the harness and the TPS input to the ECM. A 1/8W 4.7K resistor is attached to bridge the cut, and is covered with hotmelt to protect and support the resistor.
The larger capacitor is mounted on the other side of the PC board and is also supported with hotmelt.
The parts are cheap, but it is time consuming to do it well.