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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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Ok, now I understand. You were taking measurements of what I was asking for and were one step ahead of me.

Sounds like 1-4 is the one that goes to your dash. There is no active circuit there that reacts to the sensor resistor value. So it should not change with temperature.
2-3 sounds like it goes to the controller and it has a "tripping circuit" that changes state when the temperature (or resistance) hits a certain value.
Not knowing what is back there it would be hard to say if that is a problem or not.

But one thing we know is that there is no issue with your CTS or the wiring into your controller.

I think you can put aside the CTS and the wiring being problematic, they are both fine.

No pictures are necessary (at least for my understanding)
 

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Outstanding Contributor
'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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3,123 Posts
So, after those encouraging words and the normal idle I decided to dig up the air filter box, new vent pipe, and put it on. Low and behold the cold start high idle is back! I have a K&N filter, so I was suspicious. I dug up the other air filter box I have, with one damaged mounting tab, installed the still clean MB filter that I had kept, and swapped it. Still had high initial idle. (All the while I’m trying to get the Lambda just right).

Maybe an oil change is in order?

Thanks for the help.
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,500 Posts
Thanks!

I did measure the CTS cold before throwing in the towel. It seemed alright but I remember the code was for it. (HD kindly referenced it also)... I even tried to open the ECU connection and could not find the pins because no wiring diagram exist anymore it seems. (I'll try again).

But first I'll check the micro-switch. Since last I started the car it idled at 1500 RPM and my memory doesn't serve me of the test procedure I'll just press it while car is idling. (Or maybe I'll ask my son to press the pedal)...

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Did you already rule out the microswitch?

Did you check for vacuum leaks (or at least measure your intake vacuum at idle) ?
 

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Outstanding Contributor
'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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3,123 Posts
Did you already rule out the microswitch?

Did you check for vacuum leaks (or at least measure your intake vacuum at idle) ?
microswitch- While I had the intake off it idled normal so I did not test it anymore. Was that a mistake? (Sorry).

vacuum leaks- I've looked before and have a scope, I can try again.

Started the car this cold morning with my multimeter in X11 pin 2 and 3. I took pictures. High idle AND duty cycle pegged at 81.35 Hz (firm). I forget what that means, need to find the chart...

(Thank you).


(Clock is wrong in the picture).



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Outstanding Contributor
'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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3,123 Posts
80% duty cycle is for intake air temp sensor. Gonna order one and see.

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,500 Posts
You could have just measured the resistance JZ. The spec's are the same as the ones I listed for the coolant temp sensor.
It is highly unlikely the air temp sensor would make such a big difference in idle rpm. It is most likely a minor adjustment in lambda ratio,

I would check your microswitch before too long and stick a vacuum gauge on one of your intake ports. Anything less than 17 inch Hg means you have a vacuum leak.
 

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Outstanding Contributor
'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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3,123 Posts
You could have just measured the resistance JZ. The spec's are the same as the ones I listed for the coolant temp sensor.
It is highly unlikely the air temp sensor would make such a big difference in idle rpm. It is most likely a minor adjustment in lambda ratio,

I would check your microswitch before too long and stick a vacuum gauge on one of your intake ports. Anything less than 17 inch Hg means you have a vacuum leak.
Thank you for the advice.

There is a diagnostic tree to follow that I found and kind of ignored this time. First step is to measure the resistance of the sensor. I remember doing that before giving up last time. Regarding the coolant temp sensor it was also suspect per diagnostic indicator. First step measure the resistance of the CTS. 2nd is trace and verify the wiring. I could not find nor figure out the wiring even though PN helped give me a link, subscribing to AllData, and another helpful guy from Europe also tried to look. (Wish I remember his user ID, started with P I think). The MBCD was also missing the proper wiring. Hence I threw in the towel...

Strangely you seem highly doubtful whenever the car indicates this or that is the problem. (This is where we start to disagree). The first time we diverged was with the air flow pot. Even though I was confident the car was correct you were extremely doubtful. (I was driving the car in 110 F + heat and let it heat soak in the sun, likely damaging the pot). I ended up taking it out, finding two bald patches, and after testing a cheap Chinese one to no avail, patched the two spots, put it back in, and diagnostic warning light has never come back to indicate the air flow pot. This is evidence that the diagnostic indicator works as designed.

Anyways it is on order with a ton of stuff for the (other) car my wife now wants to give up. I will report (unlike some who come and go) what I find. FCP says may be as early as 1/23 when the package arrives.

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,500 Posts
The on board Diagnostic means are not very sophisticated in my '89 JZ. I doubt it is a ton better in your car. So I tend not to use it so much. It is possible that you are misinterpreting the results.

You should still make the measurements I suggested and also measure your air temp sensor even if you intend to replace it,
 

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Outstanding Contributor
'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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Thanks again.

I agree when the car stalls the error codes, in particular ones that pop up with the Check Engine light, are unreliable. If the car stalls the lights/error codes that display immediately after the stall, I have not been able to verify are true.

If the car is running and the light pops up, it is much much more reliable. In this case I have no check engine light, and the duty cycle is fixed/nonfluctuating. Car has stopped stalling, I guess it's helping itself not stall by increasing RPMs.

I had a thought while driving home after dropping my son off at school this morning. Because that cold 46 degree weather is not consistent, I may place the sensor in the refrigerator to 32 degrees, then measure the resistance. Since the new sensor is already paid for, (I'm hoping I'm right and you're wrong). But I'll follow up. It was a good 70+ degrees when I was tinkering with the car and the high idle developed, with fluctuating (no error) duty cycle.

While I wait I'll try testing the micro-switch. Not sure I understand how to test for the vacuum leak, more specifically where to connect my vacuum pump. I think I should try my best to verify those hidden IACV hoses are intact like you mentioned to search for a possible leak.

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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Best place to check your vacuum is at one of the intake manifold ports. There are 3 or more of them.
One goes to EZL via the coolant temp switch, the other to actuators for HVAC and the other to the transmission modulator (I think?) ....
Probably best to disconnect the one that goes to your HVAC at the intake manifold, not downstream at the y-connector, etc. to avoid misreadings due to benign leaks downstream.

As for the diagnostic port:

If one uses that port for diagnosis, it is only meant for the user to "go check" the component.
It is not meant for "go change" the component. Everyone, just keep this in mind.

Because more often than not the issues are intermittent due to connectors, wiring, system glitches, low voltage on the system, etc, etc, and not the actuator/sensor itself. And once the "diagnostic state" is flipped, it remains that way until the system power (battery) is removed, or someone resets it by other means.

I think you have also seen evidence of this issue in the past year so perhaps I'm preaching to the converted, but others are reading this as well.

My 2 cents worth ....
 

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Outstanding Contributor
'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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Definitely one connection goes to the transmission modulator. That was causing my shifting issues last time...

Thank you, good advice...

Didn’t get to work on the car today, at least not yet...
 

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Outstanding Contributor
'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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I just checked my FCP order status. For the temp sensor it says "DEPRECATED" and "No ETA". It's funny, but now I'm hoping you're right as these are NLA it seems!

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Outstanding Contributor
'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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4.64x kOhm and dropping! 37 F per in dash temp gauge. No wonder I felt so COLD!

It started at 4.78 kOhm roughly, would drop - 0.001 kOhm every half second I guess. Standing there waiting for a steady reading for maybe 1 or 2 minutes because of a slouched back my back started to hurt and just tried to remember last what I saw, and gave up. It's too cold for me to stand there and wait while holding the probes with my back slouched...

(I tried to bear the pain until it dropped 0.15 kOhm before I stopped, so the numbers might be off)...

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,500 Posts
It's fine at cold. Put a hairdryer on it and if you can make it go below 1KOhm or so, you're done with the sensor.

I'll steal Tom Hank's closing line on his awards acceptance speech on Golden Globes.

You've checked the sensor.....Sensor is good......
 

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Outstanding Contributor
'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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At 49 F it was 3.6 kOhm. Looks like it is consistently, although slightly, under the lower curve. I tried to order one while at an AutoZone getting intake valve cleaner and dropping of used oil and filter, but they could not special order it. I was thinking of borrowing the one from the W126.

Are you confident I shouldn't replace it?


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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,500 Posts
I mentioned this before it does not have to be that precise. If you put a hairdryer on it and it ends up being 0.5K - 1K ohms
put this one to rest. It is possible that at some point there was a glitch in the system or there was a connectivity issue.

What's on the other end of that sensor must be a simple "window comparator". If the values are out side the range it will trip.
Perhaps the comparator trip values are set at >50Kohm or <500ohm (or something similar) since ambient air is not expected to be -100c or >80c with some safety factor.

So take the measurement with the hair dryer as I suggested if you want to sleep better at night,
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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What I'm trying to say is that it will take a lot for that comparator to trip. A 5% accuracy will not do it. It will have to be off by a lot more than that.
 

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Outstanding Contributor
'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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What I'm trying to say is that it will take a lot for that comparator to trip. A 5% accuracy will not do it. It will have to be off by a lot more than that.
I’ve searching around to buy a replacement IAT sensor to be honest, but I want to thank you for your effort to help me.

You say it’s not sensitive enough to “notice” that the IAT is out of spec, but just this morning while eating my breakfast I thought, then why is it giving me 80% firm duty cycle error if it can’t detect that my IAT is actually off? I mean I actually confirmed the condition it is noting, the IAT measures below the range at two temperatures, but I’m supposed to ignore it?
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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What I was trying to relay is that that window comparator is really meant to measure if there is a connection problem (most likely). Read my response more carefully JZ.
At some point between now and whenever that comparator was tripped there must have been a one time event that tripped it. Reset it and see if it comes back.
 

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Outstanding Contributor
'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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Alright, found an intake manifold port to test vacuum. I pulled off the curved black connection and it was loose on the nipple. I pulled the other end and it was dangling! One vacuum leak found. I believe this white color plastic tubing runs to the transmission modulator. Must have busted in the middle as there's nothing on the other end.

Where do I find replacement please?

I went to the diagnostic port with blinking LED, pressed the button for 3 seconds then released. One blink. I vaguely remember that means no codes to erase. It is still 81.35 Hz firm. I guess pull the battery neg connection is the next attempt. Idle went down to roughly 800 RPM engine warmed up fully past 80 C. I shift to reverse and engine stalls. Sensor has not shipped yet like I'd hoped.

Thanks!

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