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Discussion Starter #1
so... lately the engine, on cold start, has been idling too high too long. rather than the usual 20 seconds or so, it'll do it for minutes, sometimes miles, it will remain at 1500 until it calms to 750. a shutdown and restart will sometimes make things better quicker. eventually it idles as it should.

so, I yanked the IACV



cleaned it



the hoses are in great shape



and i reinstalled it



so now, I can tell it's more 'responsive' to changes in idle as being reported by the ECU, but its still not coming down until longer than it should. there are no visible or audible vacuum leaks or leaks around my CIS housing, the OVP is new as are temp sensors 008-542-45-17 and 008-542-32-17.

the car lives in a garage, its about 50F out there, but its been in the mid 30s outside. I also validated the ICV circuit is functioning as it should by disconnecting it while the engine was running and tiggering a CEL [which I reset].

thoughts on where else to go?
 

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190E, SLK350
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I just replaced mine today too, it just felt like one of those throw parts at the car day to me.
 

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Discussion Starter #3
got in this afternoon. started the car. high idle. drove it 1 mile to the minimart. temp was creeping up off the peg. shut it down. got some stuff. got in and drove home 1 mile. by the time i'd driven the 2 mile short trip the temp gauge was reading on the first mark. the ambient temp was 48F. the idle never came down. grumble.
 

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190E, SLK350
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Did you hook up the lower hose real tight? Use a steto or a tube to listen to air
 

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'01 SLK230,'93 190E 2.3, 1971 LS5 Corvette Convertible
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2,186 Posts
yeah the hoses are on really well. i think whatever is *controlling* the IACV is bad. next stop, the microswitch.
What happens if you pull the connector off of the ICV?

Will the idle go down? Up? The same?

Now for the BIG Question....What really really really controls the ICV? ECU, Temperature Sensor, or what?

My situation is this, the only time my ICV operates is for 10 seconds when the ignition is turned on. After that, nothing! I can disconnect it and no change in idle.

And speaking of the micro switch, mine operates correctly as far as adjustment and continuity, but if I rev the engine and close the switch by hand, no change is noticed.
 

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Outstanding Contributor
'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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My wife got a car that breaks down even more than the W201, hence I am thinking about it again. (It is still insured but has expired sticker and needs a smog check).

I have a high idle too. When I pull the IACV the idle goes down, but causes a Check Engine light immediately. Got a replacement from FCP Euro but no change.

Could not figure out how to remove to replace the Coolant Temperature Sensor, have a replacement, just don't have a proper tool to replace it. Tested with a multi meter and it seemed fine...

(Yes I'm starting to throw parts at 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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Don't throw parts at it JZ just check the microswitch like the poster last said and never completed the post.
If the micro-switch is not telling the ECU to turn on idle control it will never happen.

Also measure your coolant temp sensor instead of replacing it. 2.7K cold, ~250 ohms at 85c. Dos not need to be that precise.
 

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'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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Don't throw parts at it JZ just check the microswitch like the poster last said and never completed the post.
If the micro-switch is not telling the ECU to turn on idle control it will never happen.

Also measure your coolant temp sensor instead of replacing it. 2.7K cold, ~250 ohms at 85c. Dos not need to be that precise.
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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'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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Okay, son is busy studying so I did not bother him to help me with the gas pedal.

Testing the CTS and wiring is doable by myself, CTS is 4 pin type. Four pins line up like the corners of a square. Taking measurements of the cross corners gives values that are within .05 kOhm. 2.99 kOhm and 3.03 kOhm or somewhere around there. Nothing suspicious for the ambient I feel. I cross measure the connector 1.23 kOhm and 1.27 kOhm. and match up the low with the high when I plug it back in.

Car was somewhat hard to start after sitting for many months, but starts up to just under 1000 RPM.

When engine gets up to around 60 C, RPMs fluctuate some, not rapid fluctuation, but noticable. Engine stalls. I pull the CTS connector off, measure 518 Ohm and 524 Ohm. (I am guestimating the last digits). Nothing remarkable in my mind. I then cross measure the connector. One is 1.xx kOhm, the other is -OL Ohm. Pull the probes out and air reads OL Ohm.

Huh????

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89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,501 Posts
You can put the CTS issue to rest. Those numbers are right on the money:

Temperature °C........Resistance kΩ
-20........................15.7
-10.........................9.2
0............................5.9
10...........................3.7
20...........................2.5
30...........................1.7
40...........................1.18
50...........................0.84
60...........................0.60
70...........................0.435
80...........................0.325
90...........................0.247

You probably have a MAS not an ECU.so it is not going to be pin #21 on your connector for the CTS.

You can probably check for an open or short on the wiring by looking for resistance from the sensor connector looking into wiring to the controller (ECU or MAS).
I think you did this but I could not follow your remarks.
If so, I believe no pair read zero, so no shorts, and one pair read some finite value, that is good there is some circuitry on the other end. The one that reads OL could be ok too depending on what circuit is on the other end. Although I would be a bit surprised. On that pair reverse the leads and measure again you could get another result.

I think you know how to check the micro-switch so I will not comment on that.
 

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'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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Sorry if I wasn't clear. So when the engine was cold testing the connector sockets (pins are on the CTS) it reads in the 1 kOhm range. But after the engine warms to about 60 C, the car stalled. When I measured again one was still 1 kOhm range but the other went to "-OL Ohm".

Is this normal?

Let me try again:

There are four holes. If you draw lines between two holes at a time you could either make a square, or an X. If you follow the straight lines on the X I measured resistance like that. They were both 1.xx kOhm when the engine was cold, but after stalling one read -OL Ohm. The other was a little higher than engine cold but still in the 1 kOhm range. I'm sorry if I'm vague...

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89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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Probably best make a table instead of describing the connections.

1 2

3 4


I assume when you measure 1-4 and 2-3 you are getting good results to match my table correct?

What is the next measurement? And perhaps make a table of all your results.
 

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'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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Yes, much better. Thank you so much! CTS sounds good but somehow wiring goes bad as engine warms up.

I'll try to say what happened in chronological order

Engine cold:

1-4 1 kOhm
2-3 1 kOhm

Engine warms up and idle starts fluctuating, then engine stalls. (Maybe just above 60 C on cluster).

I pull the connector and measure

1-4 1 kOhm
2-3 -OL Ohm (infinite, but somehow - )!




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Once I pull out the probes, reading goes to:

OL Ohms (infinite)

If I cross the probes it reads:

0.1 Ohm

(Multimeter sanity check).

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89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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Sorry JZ but now I'm even more confused. your original post suggested:

"Testing the CTS and wiring is doable by myself, CTS is 4 pin type. Four pins line up like the corners of a square. Taking measurements of the cross corners gives values that are within .05 kOhm. 2.99 kOhm and 3.03 kOhm "

That does not match with this:

1-4 1 kOhm
2-3 1 kOhm
 

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'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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I'm having a mental block in communication skills today...

I'm setting the CTS aside for now as we agree that it's okay.

I'm only talking about the reading from the harness/connector.

Initially it reads roughly 1 kOhm.

As the engine warmed up it started acting funny, the slowly fluctuating idle. It then stalled. I pulled the connector and decided to measure the resistances (on the connector) again.

One was roughly 1 kOhm. (1-4)

The other read "-OL". (2-3)

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If I'm not making sense I'll try to repeat tomorrow in daylight and take pictures. Somehow it develops an "open", but I have no clue why it is a negative open.

(Thank you for trying)!

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Ahh.

The 2.9 kOhm and 3.0 kOhm are reading from the CTS pins itself.

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