Idle Speed Air/Control/Slide Valve Confidence Check

[BabyBlueBenz]

As a recent acquirer of a 1986 560SL, I too have recently begun to experience the aptly described "high idle hell". I've read the related Service Manual pages and the many threads on this forum and others. I did some preliminary diagnoses this afternoon...specifically, a few tests of the Idle Speed Air Valve [ISAV] (a.k.a. Idle Control Valve, Idle Air Valve, Idle Slide Valve). I understand that there are many prerequisite items to check in resolving this dilemma, and I've done some already with more to follow in the days ahead. The attached photo shows a close-up of the ISAV (MB component ID of "Y6") currently in my car. And Yes, the 50-degree Thermovalve (labeled 7 in the photo) has been temporarily "loop-capped" as part of my EGR-removal task in progress. And Yes, I capped the vacuum fitting at the rear of the engine that lead to this Thermovalve. I will be double-checking those hidden-in-the-rear and buried-in-the-V vacuum fittings again.

As suggested at Fast Idle Issues

Originally Posted by ctaylor738

One thing to check. When you get the high idle, slide the connector off the pins on the valve a little ways, and use a meter - carefully - to measure the voltage going to the valve. If it shows somewhere around 4 volts, the relay is trying, so replace the valve. If no voltage, replace the relay.

The plug and pins mentioned are labeled "2" in the photo. With the engine warm and churning away at 1500 rpm, I measured the voltage across the pins at 3.3 volts. Does this pass? I heard this component described as a "frequency valve"...is that another way of saying it is variable control? I never heard the term used before.

Per http://www.benzworld.org/forums/r-c107-sl-slc-class/1305243-560sl-fast-idle-speed-once-engine.html:

Check the ICV's coil resistance to see if it hasn't gone open circuit first. Often they gum up and won't close fully giving you a high idle. If you lucky you can clean out the inside with alot of carby cleaner (try soaking it in it) and it may work again. An ultrasonic bath may also be a good idea.

Shutting down the engine, I removed the ISAV from its rubber-lined loop clamp along with the short rubber hoses (labeled 3 & 4) and the interconnecting rigid vacuum line (labeled 5). I cleaned these four parts with the brake cleaner "Brakleen". The interior of the ISAV and hoses were dark with soot, but cleaned up quickly. I followed the cleaning of the valve with a rinsing spray of WD-40. Once dried off, I measured the electrical resistance between the two pins and obtained 4.5 Ohms. The Service Manual specified a target range between 3.5 and 5.5, so I considered the test a pass.

Per the second page of Service Manual document 07.3-112 "Testing electronic idle speed control", I applied 12 volts to the two pins and heard a slight click. When reversed, the current yielded another click. Tom Hundt's excellent tutorial on the high idle problem at http://www.fly.net/~thundt/mercedes/high_idle_hell.htm describes the result of this test as a "loud clack" with a spring-induced click upon removal of the voltage. I did not perceive this to happen with mine. Also, the ISAV rattles when I shake it. That's my primary question here: Does the lack of spring-return and the rattle suggest a bad ISAV to you? It does to me, but I'm a newbie to these electro-mechanical systems.

For extra credit, opine on this factoid:
The last page of Service Manual 07.3-112 "Testing electronic idle speed control" contains a note regarding the "Distributor line for idle air". It details the revision of two parts related to the idle speed control system (the hose is labeled 6 in my photo). My engine number happens to fall before the implementation was made. Does anyone think these revised parts are worth pursuing?

Thanks for any and all input.