High Idle - 1990 300E

[EasyPhil]

I bought this car used over a year ago and this problem has plauged me for the entire time. I took it to a Benz Mechanic and he couldn't figure out what the problem was. I swapped that device that sits under the air cleaner with one that I know works and still no change. If I disconnect the power from that device the idle returns to what we be normal i.e. about 700RPM with the power connected it idles anywhere from 1500 to 2000RPM. If I disconnect the power from it and reconnect it the idle will return to normal, but idle fast again if the car is turned off and restarted.

I recently had to replace the overload protection relay because my ABS light was on, and my car was hard to start and would idle very roughly and eventually sort itself out. In this state the idle once the car got warmed up was always normal even with the device under the air cleaner connected. When I replaced the overload protection relay the fast idle problem re-appeared. Anyone have any ideas?

[1991300SEL]

Using the SEARCH facility, I get 91 hits on posts with the word HIGH and IDLE in the title within the TECH forum. Here's a pointer to them.

http://www.peachparts.com/shopforum/search.php?searchid=245638

[Duke2.6]

Check the throttle valve switch for proper operation. I've posted many times about this device.

Duke

[gmercoleza]

Originally Posted by EasyPhil

I bought this car used over a year ago and this problem has plauged me for the entire time. I took it to a Benz Mechanic and he couldn't figure out what the problem was. I swapped that device that sits under the air cleaner with one that I know works and still no change. If I disconnect the power from that device the idle returns to what we be normal i.e. about 700RPM with the power connected it idles anywhere from 1500 to 2000RPM. If I disconnect the power from it and reconnect it the idle will return to normal, but idle fast again if the car is turned off and restarted.

I recently had to replace the overload protection relay because my ABS light was on, and my car was hard to start and would idle very roughly and eventually sort itself out. In this state the idle once the car got warmed up was always normal even with the device under the air cleaner connected. When I replaced the overload protection relay the fast idle problem re-appeared. Anyone have any ideas?

Do a search. I cured my 300E's high idle with a fix that has been posted many times.

[EasyPhil]

1991300SEL Thanks for the suggestion about the search, been there done that, none of it applies, which is why I'm asking.

Duke2.6, do you think the throttle valve switch has something to do with it even though with a blown OVR the car never idles that high or the car never idles high if I disconnect power to the Idle Control Valve?

gmercoleza, what fix did you use? It would be helpful if you indicated what you did and what your symptoms were. Did you car idle high, but return to normal upon disconnection of power from the ICV?

[Duke2.6]

Without the idle signal from the TVS the ECU will not go into idle control mode and the result is usually a high idle speed.

Duke

[89-300ce]

Check Duke2.6's posts. I had the same symptoms as you and it was the TVS.

Jorg