Mercedes-Benz Forum - View Single Post - M103 Rough idle and vacuum leak
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post #120 of (permalink) Old 01-21-2018, 06:47 AM
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Date registered: May 2014
Vehicle: 1988 300CE
Location: Germany
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Originally Posted by KJZ78701 View Post
… I am not sure. 5k ohms seems like an odd amount. 5M ohms maybe, which for all intents and purposes is an open circuit. ...
See what I said in post 108 about that 5 kΩ connection to engine ground … and note that I mentioned “some other path“ !

Originally Posted by KJZ78701 View Post
… When I go back to the original post, I see other signs that the engine is getting too much fuel. …
The original post is almost 2 ½ years old … there‘s been some change since then.

Originally Posted by KJZ78701 View Post
… Stepping on the gas to start the car opens the micro switch, which, I believe, takes the car out of its start programming, which in most cases has fuel enrichment built in. i.e. cracking the throttle during start up actually supplies less fuel …
Please allow me to correct that. … The KE-Jetronic cold start program has fuel enrichment built in by default, not only in most cases. … And that is not switched off when the throttle, or the micro switch, is opened.

Originally Posted by KJZ78701 View Post
… Once I reread my posts quite a bit came back, including the importance of the flapper not applying pressure to the plunger in the FD while the motor was at idle. …
Please allow me to correct that too. … The AFM / FD unit is designed in such a way that the “flapper“ does apply pressure to the CP (Control Plunger) when the engine is running at idle speed … by which the CP is slightly pushed up, thus slightly opening the metering slits.

If, while the motor is running at idle speed, the CP is not slightly pushed up by the roller of the air sensor lever, then because of (at least one of) the following reasons:
- the CP can not descend all the way to the set screw (e.g. due to contamination)
- the CP set screw is screwed in too far
- the CP or/and CP guide is/are (significantly) worn
- the metering slit o-rings are worn

You said “I love your approach“. … Since I‘m a little short of time, this is currently the only thread I‘m active in, and I‘m trying to keep it systematic and to prevent confusion … and I really think that, not least in view of the hint I gave with the first sentence above, waiting for the results of the test I suggested in post 108 (possibly followed by further test steps) is in order. …

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