M103 Rough idle and vacuum leak - Page 9 - Mercedes-Benz Forum
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post #81 of 174 (permalink) Old 12-12-2017, 12:01 PM Thread Starter
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Strassenkreuzer, thank you very much for being in awe of me! You could say the DIY spirit is alive in me in general. Tinkering with electronics and robots have been hobbies of mine for a long time, so that would explain my electrical know how. I wouldn't have gotten anywhere without H.D.s diagnostic know how though. I've also had some bad experiences with mechanics with this car, so I'd rather trust myself than them!

I very much love this car. The driving experience is excellent and the aesthetics are timeless, in my opinion anyway. I've never had a need for more performance when running right. My grandfather drove her for much of my childhood, and gifted this car to me in high school when I went with him to purchase his new car. We completed a number of projects on it and he has recently passed, so there is plenty of sentimental value in driving and working on it.

My car does burn/ leak oil. It's been a while since I consistently drove so I can't quite say how much. Based on the stamped card in the driver's door panel the birth date is 11/88.

Now what you've all been waiting for... The distributor cap and rotor worked! The start up is easier than it's been in a long time, starts with little crank time and little or no depression of the throttle. However the idle and performance are still a bit off. The idle is a little on the low side, around 500 rough choppy and "hunting" for the correct speed as it's been for a while. When cold there's a significant lack of power. Putting the throttle to the floor from stopped or rolling results in the engine bogging down and loosing RPM. For maximum power I need to hold the throttle at around 80%. When warmed the idle is roughly the same, but the lack of power is no longer present, and full throttle results in full power. I've only had a couple of chances to drive the car so there's a small sample size for these results, but this is what I've noticed so far.

So @H.D. , what's the next step?
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post #82 of 174 (permalink) Old 12-12-2017, 03:09 PM
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Quote:
Originally Posted by codycool55 View Post
... The distributor cap and rotor worked! The start up is easier than it's been in a long time, starts with little crank time and little or no depression of the throttle. ...


As the next step, I come back to my last sentence in post 67:
Quote:
Originally Posted by H.D. View Post
... If that‘s in order (ignition coil & distributor) I‘ll come back to the suspect I mentioned in posts 53 and 55 ... the EHA ... and explain in detail how to check it.
… all the more after what you report now … (“When cold there's a significant lack of power. Putting the throttle to the floor from stopped or rolling results in the engine bogging down and loosing RPM. For maximum power I need to hold the throttle at around 80%. When warmed the idle is roughly the same, but the lack of power is no longer present.”)

But, before I explain in detail how to check the EHA (actually the whole function chain “o2 sensor / ECU / EHA”), I suggest to first check if the CIS-ECU receives correct information from the CTS (Coolant Temperature Sensor) like this:
When the engine is cold (and not running), disconnect the 25-terminal ECU connector and measure the resistance between terminals 21 & 2 and between terminals 21 & 20 (see attached drawing). ... When you report the resistance, please report the temperature at which you measured it too.

Disconnect / reconnect the ECU connector always with the ignition switched off !

BTW, the question about the play of the AFM plate is still open, right? … How much play is there between its zero position and the point where you feel the first resistance from the CP ?

And with your car‘s production date being 11/88, I suggest to open the valve cover and visually check the camshaft lobes. … If your car burns oil and the valve stem seals have never been replaced, you should consider replacing them.

H.D.
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post #83 of 174 (permalink) Old 12-13-2017, 11:17 AM Thread Starter
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I believe that is the wrong ECU connector. Mine has 35 pins although a number of them have no terminals. See attached. When perfoming the test should the key be in the on position or all the way off?

As for AFM play, there's under 1 cm of play. Maybe around .8 cm?
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post #84 of 174 (permalink) Old 12-13-2017, 12:58 PM
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I believe that is the wrong ECU connector. Mine has 35 pins although a number of them have no terminals. ...
Yes … it looks like your car is equipped with ETA (Electronic Throttle Actuator) and your picture shows its 35-terminal ECU. … The CIS-ECU is located in the passenger footwell (see attached picture).

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Originally Posted by codycool55 View Post
... When perfoming the test should the key be in the on position or all the way off? ...
All the way off !

Quote:
Originally Posted by codycool55 View Post
... As for AFM play, there's under 1 cm of play. Maybe around .8 cm?
I thought I should ask that question about the AFM play again. …

If the AFM plate really has that much play (8 mm), then, with the high EHA current in your videos, the Lambda adjustment screw is turned extremely far ccw, causing what I mentioned in post 55 … a fuel/air mixture extremely lean beyond the system‘s enriching limit via EHA control ... which, along with the weak ignition, causes the low o2 sensor voltage in your videos, as I explained in post 55.

You’re sure it’s .8 cm, and not .8 mm ?

Please reread the test procedures in post 39, especially the part where I said:
“Then, latest after about 2 mm !, you should feel the other end of the AFM lever reach the CP.”
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post #85 of 174 (permalink) Old 12-14-2017, 04:27 PM Thread Starter
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What is the purpose of the ETA? I always assumed that was the CIS-ECU.

I was unable to record a resistance or connection between terminal 20 and 21 or terminal 21 and 2. This is at a temperature of about 32 F. I visually inspected the sensor and it appears that at one point the plastic shroud around the sensor had been broken, and the terminals had been surrounded in electrical tape! I've been looking for this part online since discovering this but I've been unsuccessful. Does anyone have a source for these type of parts or is this a junkyard part?

I measured the play today, and it was at just over 1/4 inch. So yeah, around 7-8 mm.
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post #86 of 174 (permalink) Old 12-15-2017, 10:32 AM
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What is the purpose of the ETA? I always assumed that was the CIS-ECU. ...
As the name “Electronic Throttle Actuator” suggests, the ETA controlls the throttle valve electronically. …

Quote:
Originally Posted by codycool55 View Post
... I was unable to record a resistance or connection between terminal 20 and 21 or terminal 21 and 2. This is at a temperature of about 32 F. I visually inspected the sensor and it appears that at one point the plastic shroud around the sensor had been broken, and the terminals had been surrounded in electrical tape! I've been looking for this part online since discovering this but I've been unsuccessful. Does anyone have a source for these type of parts or is this a junkyard part? ...
If there is no connection (infinite resistance) between terminal 21 & 2 and between terminal 21 & 20, then there is a problem with at least one of the following:
- CTS (Coolant Temperature Sensor)
- connection of the CTS to the ECU connector (wire / plug)
- connection of terminal 2 to engine ground (wire / plug)
- connection of terminal 20 to ground (wire / plug)

That CTS (B11/2, see attached drawing) is a double sensor. On your 300SE (produced 11/88) there should be two separate plugs connected to it (one with a green/black cable and one with a green/red cable). One goes to the ignition control module, the other one goes to terminal 21 of the CIS-ECU. Which of the two pins which plug / cable is connected to doesn’t matter.
To check the sensor itself, measure the resistance from each of its two pins to engine ground twice … once when the engine is cold … once when the engine is at operating temperature.

Quote:
Originally Posted by codycool55 View Post
... I measured the play today, and it was at just over 1/4 inch. So yeah, around 7-8 mm.
Not to blame you, but to illustrate the value of correct / precise reporting:
In post 39 I suggested some tests on the AFM, which included checking its play and I said that the play should be 1-2 mm and “latest after about 2 mm! you should feel the other end of the AFM lever reach the CP.”
In post 40 you replied:
“I tried all these tests and they've all been passed … “

Very early in this thread I mentioned the possibility of a problem with the FD‘s basic setting via Lambda adjustment screw, which seems to be the case here. Obviously someone messed with that screw. … And it looks like a case of neglected maintenance. …

Let’s first take care of the problem with the CTS signal … and get prepared to switch your California version CIS-ECU to duty cycle output to the round diagnostic socket X11 according to 07.3-0121 pg 97/98, as mentioned in post 55.

H.D.
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post #87 of 174 (permalink) Old 12-15-2017, 11:32 AM Thread Starter
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Quote:
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As the name “Electronic Throttle Actuator” suggests, the ETA controlls the throttle valve electronically. …
Well yes of course.. I suppose a better question would be when would the throttle need to be electrically actuated? To my knowledge when I depress the gas pedal it is mechanically actuated. Does ETA kick activate when the cruise control is active?

Quote:
Originally Posted by H.D. View Post
That CTS (B11/2, see attached drawing) is a double sensor. On your 300SE (produced 11/88) there should be two separate plugs connected to it (one with a green/black cable and one with a green/red cable).
My sensor appears to be a little different. There are 4 pins coming from the sensor, and one terminal with connectors for those 4 pins. I've attached an image

Quote:
Originally Posted by H.D. View Post
Not to blame you, but to illustrate the value of correct / precise reporting:
In post 39 I suggested some tests on the AFM, which included checking its play and I said that the play should be 1-2 mm and “latest after about 2 mm! you should feel the other end of the AFM lever reach the CP.”
In post 40 you replied:
“I tried all these tests and they've all been passed … “

Very early in this thread I mentioned the possibility of a problem with the FD‘s basic setting via Lambda adjustment screw, which seems to be the case here. Obviously someone messed with that screw. … And it looks like a case of neglected maintenance. …
Feel free to place the blame where blame is due! I must have read that as 2 cm.. my mistake! At one point I had a mechanic recommend I mess with the screw to optimize the idle.. and being a naive teenager I listened. I later had a different mechanic state he reset it and I should never mess with it. There is certainly a case of neglected maintenance on my part
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post #88 of 174 (permalink) Old 12-15-2017, 12:57 PM
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... when would the throttle need to be electrically actuated? To my knowledge when I depress the gas pedal it is mechanically actuated. Does ETA kick activate when the cruise control is active? ...
Yes, the ETA is used for cruise control and ASR.

Quote:
Originally Posted by codycool55 View Post
... My sensor appears to be a little different. There are 4 pins coming from the sensor, and one terminal with connectors for those 4 pins. ...
Hah! … Maybe that has to do with the fact that your car is a California version. … No wonder you saw infinite resistance between ECU connector terminal 21 & 2 and 21 & 20.

In that case, please measure the resistance between ECU connector terminal 21 & 7 ... with the 4-terminal plug connected to the CTS … and when you report the resistance, please report the temperature at which you measured it.

Quote:
Originally Posted by codycool55 View Post
... At one point I had a mechanic recommend I mess with the screw to optimize the idle.. and being a naive teenager I listened. I later had a different mechanic state he reset it and I should never mess with it. ...
LOL … he was right to say you should never mess with it … but it seems he “messed” with it himself. …
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post #89 of 174 (permalink) Old 12-15-2017, 02:15 PM Thread Starter
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Resistance between 21 and 7 was 5.85k ohm at about 33 F
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post #90 of 174 (permalink) Old 12-15-2017, 03:46 PM
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Resistance between 21 and 7 was 5.85k ohm at about 33 F
Perfect … that‘s close to the center of the target range at that temperature, provided that the engine had completely cooled down when you measured it.

It‘s past midnight here … I‘ll come back with further procedures later.

Remember the last sentence of post 86, before we touch what‘s misleadingly called “mixture adjusting screw“. …

H.D.
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