W116 Euro 350SE rough idle - Mercedes-Benz Forum

LinkBack Thread Tools Display Modes
post #1 of 1 (permalink) Old 08-16-2012, 07:17 PM Thread Starter
BenzWorld Junior Member
atatexan's Avatar
Date registered: Aug 2005
Vehicle: 1975 W116 350SE + 2002 R170 SLK320 6-speed
Location: Dallas, Texas
Posts: 27
Mentioned: 0 Post(s)
Quoted: 1 Post(s)
(Thread Starter)
W116 Euro 350SE rough idle

My car, a Euro 350SE, 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.

2002 R170 SLK320 6-speed
1975 Euro 350SE
1992 Lexus SC300 5-speed (gone)
2004 Audi S4 (gone)
1986 190E 2.3-16 (gone)
1987 300SDL (gone)
1994 E420 (gone but not forgotten)
1968 250SE (long gone)
1962 220S (long gone)
atatexan is offline  
Sponsored Links

  Mercedes-Benz Forum > General Mercedes-Benz Forums > Vintage Mercedes-Benz

Quick Reply

Register Now

In order to be able to post messages on the Mercedes-Benz Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Title goes here

video goes here
description goes here. Read Full Story
For the best viewing experience please update your browser to Google Chrome