Peter,

Man, you guys are good. Thanks for your post, but I think I led you down the worng path with my inability to accurately name these parts, so let me try again.

I first checked the usual suspects: the air intake on the cold start valve is fine, the actuator inside that mechanism works fine (I tested using the method in recommended in the prior post: after removing the air filter, there is strong suction with engine running cold, very light suction when running warm and blocking off this intake has no effect on RPMs of warm running engine). Also rechecked timing and vacuum advance, all good.

Now for the answer: The throttle blade (what I called the butterfly valve, but what the heck, I am old enough to know how to work on real carbs) was fully closed under cold and warm running conditions. But there was ZERO play in the connecting rod (what I called the actuator). But with hot car, the connecting rod located directly above the hottest part of the car (even with properly installed manifold shield) the rod actually lengthens enough--all it took was .003 inches or so (I believe that's about the width of the cigarette wrapper you mention) -- to push open the throttle blade and cause the raised idle. And the hotter the engine, the longer the rod, the wider the gap and the higher the idle. Accounted for a maximum increase of up to 500 RPMs.

Now that no one is still with me, let me go on. Did you ever see the glass tubes of mercury in a pendulum of an antique clock with a metal pendulum rod? They are not there for show. They are there to keep the moment of the pendulum constant: As ambient temperature rises, the mercury rises in the tubes, and thereby offsets the effect of the temperature on the LENGTHENING OF THE PENDULUM ROD. Longer pendulum makes "center of gravity" (moment lower) which would otherwise slow the clock. But this is offset by the rise in mercury that puts more weight toward the top of the pendulum. Yep, its true.

Thanks,
g

__________________
64 230sl, my daily driver
94 E500, sold
98 E320, family and dog hauler
04 C240, safe machine for teen drivers, but a poc
08 audi a4, yes we have gone to the dark side