Mercedes-Benz Forum - View Single Post - M103 Rough idle and vacuum leak
View Single Post
post #49 of (permalink) Old 09-29-2017, 04:11 PM
Outstanding Contributor
H.D.'s Avatar
Date registered: May 2014
Vehicle: 1988 300CE
Location: Germany
Posts: 1,360
Mentioned: 36 Post(s)
Quoted: 515 Post(s)
Originally Posted by codycool55 View Post
Sorry for the long delay in reply, I've just moved back to college for the quarter and I have been very busy ...
Don‘t worry! ... and don‘t feel urged to do these simultaneous tests if that causes inconveniences. I only introduced them because they‘re very informative and help to reduce troubleshooting time significantly … and they‘re part of my basic KE-Jetronic test procedures.

Originally Posted by codycool55 View Post
... my EHA amperage was 25ma with the key off, and with the engine idling was -14 to -15 ma ...
Assuming that you mean “with igniton on, engine off“, I suggest to check the resistance between both EHA pins (should be 18 – 21 Ω).

EHA amperage of -14 to -15 mA with the hot engine running at idle, as well as the 0% duty cycle you reported earlier, point to “too little residual oxygen in the exhaust gas” … provided that all components work well! … Can be caused by a fuel/air mixture that’s rich beyond the system’s leaning limit (in case of M103: -10 mA) for a number of possible reasons (of which wrong Lambda adjustment via adjustment screw is only one) … or by weak / incomplete combustion. … But there could also be a problem with the o2 sensor, falsly reporting “too little residual oxygen in the exhaust gas” … or with the ECU, falsly processing the o2 sensor’s input … or with the EHA, not properly following the ECU’s order … or with the FD, not properly following the EHA’s order … or with the injectors, not properly following the FD’s order, …

… and, especially since the o2 sensor voltages you reported earlier are not in line with this EHA amperage, that’s where the above-mentioned simultaneous tests would come in handy, in order to narrow down this list of possible culprits significantly … possibly down to wrong Lambda adjustment (screw turned to far cw) … or they might point to other suspects, like igniton components. …

The resistance between each pole inside the distributor cap and the respective spark plug connector should be ~ 2 kΩ. The rotor should have ~ 1 kΩ. Between the cap’s center pole and the end of the wire that’s connected to the coil should be < 1 Ω. The coil should have 0.3 - 0.6 Ω between terminal 15 (big hex nut) and terminal 1 (small hex nut), and 8 – 13 kΩ between terminal 1 and the high voltage terminal.

Btw, in your initial post from two years ago you mentioned that you have to depress the gas pedal to start the car. … Is your car equipped with EGR (exhaust gas recirculation)? … If so, make sure there is no EGR related false air involved … might be caused by a stuck open EGR valve, which can not be spray tested.

I assume you made sure that the AFM‘s zero position and play are correct and that the AFM / CP movability is good.

Originally Posted by codycool55 View Post
... there's a mechanic I have had experience with and seems to know his stuff, and a Mercedes dealership nearby. If I chose to take it to a mechanic or dealership, is there anything specific I should tell them to look for?
You might tell them to have a look at this thread. …

H.D. is offline  

Title goes here

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