I recently went through a process with a mercifully happy outcome. The auxiliary air valve AND throttle positioning sensor failed. No longer available. Through the glory of the internet I was able to solve the problem.

Anyone care to hear the details?

__________________
Charles Cleaver
1975 350SE + 1992 300CE-24 SportLine 5-speed + 2002 SLK320 6-speed + 1974 W114 280
1986 190E 2.3-16 (Decomm rear self-leveling suspension; Euro-code headlamps) sold
2004 Audi S4 6-spd - sold
1969 (2) and 1980 Porsche 911T, S, and SC - alas gone
1987 300SDL - Graf Spee; Euro-code headlamps; 16-inch 8-hole wheels - sold
1994 E420+(E500 suspension/E-code headlamps/PAD chip) sold
1968 250SE 4-speed (NICE car) - long gone
1962 220S 4-speed/column mount - long gone

Fire away, i'm always interested.

Good luck

My car, new to me in May, had a surging idle, very lumpy, with lots of smelly unburned fuel coming from the tailpipe. Mileage was grim.

Father-in-law who is a 35-year certified M-B tech remembered the US-spec 450SE/SEL's had wear issues with the Auxiliary Air Valve (sits on the front top of the engine and acts like a temperature-sensitive choke) and Throttle Positioning Sensor (located passenger side of throttle body). Because the AAV was frozen and did not move up or down as the engine warmed, these were the assumed culprits.

Part numbers identified but we soon discovered they were "NLA" (no longer available) through Mercedes. Fortunately our own Peach Parts has an LA-area vendor that rebuilt my Euro-spec AAV within a week. $340. Hurray, Phil Reinhart.

The TPS was another matter. This bizarre little antiquity has a gold foil circuit that transmits throttle postion (from the flap on the throttle body) to the primitive D-Jet brain. A post on w116.org mentioning TPS problems mentioned a guy on the Porsche 914 forum who rebuilds them. Very nice, clever guy is David Sprinkle. He agreed to copy the foil piece onto a new "circuit". Turns out the 350SE uses the exact same TPS as a 1.7 litre 914. Had mine rebuilt and returned within a week for $100.

We had to experiment with adjusting the TPS a bit with an ohm meter. Once installed, idle totally straightened out and the car runs as it was designed to do. Thank Heavens for the internet search engines and the ability to keep these cars running.

__________________
Charles Cleaver
1975 350SE + 1992 300CE-24 SportLine 5-speed + 2002 SLK320 6-speed + 1974 W114 280
1986 190E 2.3-16 (Decomm rear self-leveling suspension; Euro-code headlamps) sold
2004 Audi S4 6-spd - sold
1969 (2) and 1980 Porsche 911T, S, and SC - alas gone
1987 300SDL - Graf Spee; Euro-code headlamps; 16-inch 8-hole wheels - sold
1994 E420+(E500 suspension/E-code headlamps/PAD chip) sold
1968 250SE 4-speed (NICE car) - long gone
1962 220S 4-speed/column mount - long gone

Those AAV are a pain alright, but are at least mechanical so there is a chance of a homemade repair, as for the other 'bizarre little antiquity' that would be way beyond my capabilities and it's handy to know that, that fella on the 914 forum has a solution, they are the sort of parts which are now getting rarer and more expensive over here, thanks for the information.

Good luck