I am restoring a 71 W114 280CE with 69k on the clock. It has the Bosch D Jetronic system, and wont cold idle. Starts no problem, will idle when reaching normal temp and is ok warming up if you keep the throttle pressed to a fast idle. When warm idle is managed ok when engaging auto drive, reverse etc. Looking through all the normal wisdom would point the the aux air valve being stuck. Since this is a serious access job to get to it on the block side, I wanted to be sure, so when the engine was cold I: 1. Disconnected hose on air cleaner side of flap and blew down and there was no resistance 2. Tipped some Redex down to try unsticking vale, and it dropped out onto the ground - so that tends to dismiss test 1! 3, Found connection to inlet manifold on other side of flap valve (next to a temp sensor?) and tried the suck test and got air flow. Also tipped Redex down that pipe and it didn't fall out! What confuses me is that when cold I expect the valve to be open, and close as block temp increases to a point where it iss hut at normal temp (only air path through throttle flap). Trying engine with inlet manifold connection disconnected (wide open to air) no cold idle. Block up inlet (no additional air introduced to manifold) and engine idles cold exactly right, even when auto engaged. Now that's the opposite to what I was expecting! Really need to get this right as extracting this valve is not going to be straight forward! Looked at it from top and looked at it from bottom. I have removed the air cleaner to try and clear a path from the front of the engine bay. Unless anyone has a smart trick, it looks like it was designed as an engine out service part! Would be grateful for someone to check my logic (or lack of) to preserve my sanity.