1995 Mercedes E320 cold start issue

[gregoron]

The car idles rough when the car is started cold in the morning. Cold in Hawaii is 65F. There is also a clicking noise where the idle speed control / cruise control module located in the false floorboard of the front passenger. The non-electronic throttle body (Non-ASR ETA) also clicks simultaneously with the ISC/CC module. The RPM hunts between 500-1000 RPM only for 3 minutes then stabilizes to 600 RPM.

When the engine warms up to 60C via the temp gauge, the clicking stops and the engine runs and restarts fine all day. Then it's the same clicking next morning. I also have a check engine code 17 indicating a data exchange error between modules.

Cruise control works. The biodegradable wiring harness has been changed. The over voltage protection relay was tested and works fine. All fuses were replaced. Engine coolant and air intake temperature sensors were replaced.

I've asked in MB forums and they suspect either the original throttle body with the biodegradable wiring insulation or the ISC/CC module. I don't think it's either though because the symptoms does not tally with a typical non-ASR ETA failure which includes loss of cruise control and erratic engine idle at all temperature. I also checked the ISC/CC module's CAN resistance value and it is fine. I think it's an electrical issue that's temperature dependent.

Any inputs from anyone with experience on these cars?

 

[Trav]

Does the engine start well or are the cranking times longer than usual?
I see you have looked at all the usual suspects. this is a cold start issue only correct?

 

[gregoron]

Originally Posted By: Trav
Does the engine start well or are the cranking times longer than usual?
I see you have looked at all the usual suspects. this is a cold start issue only correct?


Yes on both questions. Engine starts quickly and runs well. The issue only happens on cold starts. In fact, the engine runs and idles smoothly when it's warm and at normal operating temperature.

I forgot to add that the battery is new and is getting charged sufficiently. I don't have any battery drain too.

 

[Trav]

It would seem to break down to either the ISC or throttle valve potentiometer, those are the MB OB15 codes
Is the code 17 you get a pin 8, pin 14. Did you reset and reactivate the ECM after doing the repairs?

 

[gregoron]

The code 17 is from the built in diagnostic board with the button and blinking LED. I also checked pin 8 (HFM SFI) and pin 14 (ISC/CC) with my homemade DTC LED reader and no codes. I have reset and cleared code 17 and it came back.

By the way, my AC stopped working a month ago when this clicking started to happen. The compressor is seized. No code from the AC pin though.

 

[Trav]

Thinking about this a little more if the problem was in the ISC or throttle valve pot it would probably effect it warm also.
Have you tried pulling the A/C relay and fuse just to see if it makes any difference?

 

[gregoron]

Thanks Trav. No I haven't. I'll try that today.

That's what I think so too. A bad potentiometer or wiring in the throttle body would affect warm temp idle and cruise control too, which it doesn't. So it's either the ISC/CC module, AC relay or module, or MAF. These components get info from temp sensors.

 

[Trav]

I would suspect a MAF issue would also effect the warm engine but who knows some strange things can occur with these systems. I can see the A/C circuit effecting the ISC, the ticking is sending me that direction.
Keep us posted, its hard to diagnose something like this on a forum but with any luck you can to the bottom of this.

 

[gregoron]

It turns out that this model has no dedicated Klima relay. It has the Klima/Kickdown (AC compressor Cutoff at full throttle) relay part no 003 545 56 05. The compressor goes through Fuse 7 which also powers a lot of mechanical components. I replaced that fuse already with copper/ceramic ones.

Anyways. I'll test the Kickdown relay this weekend.

I also noticed that humidity plays a part in the ticking noise. When I start the car in the afternoon when the interior is warm, there is no ticking noise from the ISC/CC module. The engine idles smoothly at 1k RPM and I hear the secondary air pump working. It's in the morning when the cabin is cool from the evening that the ticking and rough idle appear. Also the air pump doesn't work. Strange. It might be reacting to some condensation somewhere.

 

[gregoron]

Update: I took the Klima / Kickdown relay out and started the car in the morning. It started fine but the ISC/CC module still clicked and idle was rough. I reinstalled the relay and the same thing happened. This leads me to conclude that it's the ISC/CC module that's defective even though the resistance between the CAN pins (44 & 46) were within normal range at 120 Ohms. I did open up the module and nothing seems abnormal visually. There is a small relay inside and that may be the problem since that's the only part that should be clicking in there.

I'll replace the module then update my results here. If that doesn't solve it, then I'm looking at a throttle body (ETA) rewiring or replacement.

 

[gregoron]

Update: I replaced my non-ASR CC/ISC module and I think that my problem is solved. I no longer get the clicking noise from the module and non-ASR throttle actuator on cold starts. My error code 17 from DTC pin 3 went away. In fact I no longer have any error codes on pins 3, 7, 8, and 14.

I'm just glad that it isn't the throttle actuator yet. I had to buy a used CC/ISC module from eBay for around $116 including shipping. After installing it, I had to clear two error codes (5 and 11) from CC/ISC pin 14. They never came back.

The LED error code reader was indispensable. It allowed me to diagnose the problem to the module and not the actuator. I highly recommend using this tool. Thanks for all your help Trav.