Engine Idle Relay & Exploring the Passenger Footwell

Last week I went to visit a friend who also has a 560 SEC, and borrowed his engine idle relay. The high idle speed problem was not fixed, but the effort wasn't a complete waste: it appears my idle relay is functioning correctly, or both of ours are broken. Anyway, next in the saga of high idle speed I will again be looking at the Idle Air Control Valve.

The idle relay is housed in the passenger footwell, next to other electronic equipment such as the OEM alarm system, Webasto control unit and stereo cabling. This space is covered by a plastic "kickplate" that is tightly fastened to the firewall with a plastic nut. The floormats rest atop the kickplate. While we were swapping idle relays, I found that my kickplate had gone missing at some point in the cars life. I turned to my trusted W126 spare parts guru and he sent me a mint part along with the special plastic nut. Here's some pictures of what a W126 footwell looks like. Note that mine has a lot of non-OEM cabling for the retrofit alarm and stereo.

On another topic: We looked at the W126 microfilms and it appears the OEM radio for this car was indeed the Becker Mexico Cassette Diversity. The Diversity was a revised model of the Mexico Cassette unit, and was introduced in I think 88 or 89. It was the first radio with a dual tuner and featured, for example, automatic volume adjustment for vehicle speed. The radio reads a signal coming from the speedo. These radios are pretty rare to find as standalone units, usually they have to be sourced from a "spares" car. Refurbished units in retail can go for as much as 500 EUR. On eBay, they cost anywhere from 150 to 300 EUR depending on condition and accessories. I may have a chance of sourcing one with a minor technical issue from a forum buddy for about 140 EUR but this remains to be seen.