Intermittent Tach and fast idle(cold start) system
 

RE: 1988 w201 diesel (190d) idle control and tach failure

Howdy all,

Okay my wife's car is acting up. On start up, the car's cold start/idle control system does not work, and at the same time the tachometer does not work. Then after some time, from a few seconds to a few minutes, both systems start to work at the same moment and work perfectly.

Oh, and the dash clock has stopped working as well. But it failed a few weeks ago and has never returned to life.

Thanks in advance!
John

On my 300D the L3 starter ring gear sensor provides a signal to the computer to control idle speed and to the tachometer.

Check to see if yours is disconnected or bad. You have a 2.5L, right?

If you have a voltmeter you can check to see if it supply's > 2.7VAC at idle. If not, MB says to replace it.

Sometimes the tip can get dirty and they say to clean it first and retest if it fails,

Yes, its a 2.5L 602 engine, very similar to yours but not turbocharged.

Sounds like a plan. Where is the ring gear sensor located on your engine? Though it might be different on the 190d, I'll start looking there.

Thanks.

They should be very similar. Check page 5 of this document.

http://w124-zone.com/downloads/MB%20CD/W124/w124CD1/Program/Engine/602_603/07.1-2006.pdf

The sensor is located on the driver side of the engine just forward of the bell housing.

But the connector to test at is located under the hood, passenger side, near the battery.