Need help diagnosing stubborn idling issues

[teh]

Hi everyone! I need some help in getting my 525e (04/86) running right.

Let me preface by saying that I know that idle issues are very common on these injection systems and I have probably read all threads about this topic on here as well as other forums. I now have a good general understanding of the system and which components are involved. However my diagnosis so far was not successful in finding the culprit.

Let me also say that I know that the Idle Control Valve or the Idle Control Module are often the cause of these problems. I would love to simply replace both, but they are either very expensive or in the case of the Module simply not available new or rebuilt where I live.

The Problem: Intermittent surging idle + constant high idle (I have no tach, but sounds like around 1500 rpm). Both only happen once the engine is fully warmed up. Runs fine otherwise.

What I have done/checked so far:

• Checked, cleaned and readjusted fuse no. 6

• Thoroughly cleaned and lubricated the ICV (seems to by very snappy when manually applying 12V, buzzing when ignition is switched on)

• Swapped the Idle Control Module against a supposedly working used unit (not ideal I know but I don't have access to a new or refurbished one)

• Checked the 45° temp switch (this one was faulty. Since it is NLA I build a replacement myself which tests fine. After the replacement the surging was gone for a while, but has now returned but the switch still tests fine...)

• Checked the 0° temp switch (did not check if it will close below 0°, but above its open)

• Blue Coolant Temp Sensor (Mine was white and seemed fine but changed just in case since it is cheap and I had one fail on another car before)

• Checked brown Coolant Time Switch (Resistance seems to be in spec, not sure if this has potential influence on idle or not)

• All vacuum lines including J boot are new (I will smoke test again just to make sure but I think there is no vacuum leak)

• TPS "clicks" right on closing or opening the throttle

• Checked all connections to the Idle Control Module for continuity (*)

* the only thing I can't confirm is pin 7 "Neutral Input (Manual Transmission)" as seen here:

Pin 12 should have 12V when the car is in neutral? Where does this come from? Is there a switch somewhere?

The Idle Control Module still seems to be the most likely culprit at this point. How ever since I cannot buy one or would have to order a refurbished one from the US most likely which is very expensive, I want to be sure it is the cause of the problem. You read about these modules failing a lot but nowhere I could find what is actually failing inside of them. Today I opened mine up to look inside. My PCD diagnosing skills are limited and I cannot spot anything obviously wrong with it. I have access to a high quality multimeter and other tools if anyone can instruct me on what to test I might be able to do it.





Any further ideas are greatly appreciated.

[turbodan]

The neutral signal is supplied by the same switched 12v source that powers the control unit. Looks like it goes through a short loop of wire at the connector.

About all I've ever been able to do with a printed circuit board is re-flow the solder joints. Sometimes this does fix issues caused by cracked joints.

[Aldo525]

My experience in M20 ICV is even though you hear the buzzz, the valve is not good. Try another one that is known to be ok. By connecting and disconnecting the ICV plug, do you notice any difference in idle??? A test I did with an M20B25 (e34 525i) was start the engine when cold (engine running well at idle), disconnect the ICV plug and wait until engine is warm, then reconnect the plug......if the revolutions increase, your problem is a defective ICV.....I tried a new german Löwe ICV, good when cold but idle increase when warm, then a chinese unit...disaster!!!....finally I paid the expensive OE Bosch and the engine runs like new.

Re: "brown Coolant Time Switch".....check if the Cold Start Valve is open all the time (delivering fuel all the time).

Re: "TPS "clicks" right on closing or opening the throttle".....check continuity between term 2 and 18 (throttle closed) & 3 and 18 (almost fully open). Just "click" is not enough to assure the TPS is ok. Also measure at least 5V at the ICV plug (ignition ON)

[teh]

Thanks for your replies. I have a some updates. First here is a link to the only write up of someone who found something wrong with the ICM and was able to fix it. Might be helpful to others. http://www.unofficialbmw.com/repair_faqs/idle.html I did not find the same issue with mine.

What I did find out is the following:

I started the car without the ICM connected and the idle began surging right away (engine cold) and the surging was much stronger than before. Revs would go up to >2.000 I would guess. The surging I had before only happened when warm, and were much less intense.

I removed the ICV again and gave it an other cleaning. This time I flushed it with brake clean multiple times, trying to manually move the plunger(?) inside carefully with a screwdriver and clean inside with cotton buds. Afterwards I flushed it multiple times with WD-40. This seems to have helped since it idles much better now. Most of the times the car has an idle around what I would expect. However it is not completely fixed yet sadly. After driving on the highway for some time and going back the idle is quite high again, sometimes going down after a big of idling, sometimes not... once or twice it also went back to surging... I can't really wrap my head around why this would happen... Any ideas?

Anything else I can do with the ICV to make it move better? The VDO two pin version (13411709898) seems to be completely NLA now...

[Aldo525]

Two pins ICV???....I thought that version of ICV (13411709898) was used in older versions of e28.

Anyway, If the valve has 2 pins, I would look for the Mercedes Benz Bosch alternative 0280140510 but in some L shape version if necessary.
That valve has a regulation screw for the air passage and by regulating that screw your idle problem could be solved.

I know this MBenz ICV because my e28 525i had it installed when I bought it to replace the original valve which is a Slide type (my car is the L Jetronic) and what they did was connect the MBenz ICV to an on/off switch on the center console and that it was used (on) when the car was started when cold and then turned off and remained in idle, according to the adjustment of the screw. It was strange but it worked very well.

Now in your case, if the car has the two-pin plug for the ICV VDO it may be (hopefully) that an MBenz Bosch valve works without a problem and you are also left with the possibility of the air opening screw. These MBenz valves are not expensive.....

[turbodan]

The old fashioned fix was a penny with a hole drilled in it, installed as a restrictor in the ICV inlet hose.

[Mike W.]

Two pins ICV???....I thought that version of ICV (13411709898) was used in older versions of e28.

I believe 2 pin ICVs were used in 533s and 528e's until the 88 super e. Since OP has a 525e, not the US version, I don't know which he would have, but I'm guessing the early, 2 pin one.

[teh]

Two pins ICV???....I thought that version of ICV (13411709898) was used in older versions of e28.




 

I believe 2 pin ICVs were used in 533s and 528e's until the 88 super e. Since OP has a 525e, not the US version, I don't know which he would have, but I'm guessing the early, 2 pin one.

I am back to working on this issue. Yes I do have a two pin ICV which I think is standard for 525e. Part number should be 13411707395 or 13411709898. The writing on mine is gone so I am not sure which one. 

Two pins ICV???....I thought that version of ICV (13411709898) was used in older versions of e28. 

Anyway, If the valve has 2 pins, I would look for the Mercedes Benz Bosch alternative 0280140510 but in some L shape version if necessary.
That valve has a regulation screw for the air passage and by regulating that screw your idle problem could be solved. 

I know this MBenz ICV because my e28 525i had it installed when I bought it to replace the original valve which is a Slide type (my car is the L Jetronic) and what they did was connect the MBenz ICV to an on/off switch on the center console and that it was used (on) when the car was started when cold and then turned off and remained in idle, according to the adjustment of the screw. It was strange but it worked very well.

Now in your case, if the car has the two-pin plug for the ICV VDO it may be (hopefully) that an MBenz Bosch valve works without a problem and you are also left with the possibility of the air opening screw. These MBenz valves are not expensive.....

 

 

I found and bought this ICV (eBay) made for W126 V8. It was the only 2-pin "L-shaped" one I could source. I tired it out but no luck so far. With it installed the idle is very high even when cold. I guess it might let more air through because it is made for a higher displacement engine? I tried the adjustment screw but it did not change anything. However I have found this video: https://youtu.be/hbQcWBykjbc?si=FPGkK9aoh7jsbdt4 and I think I the adjustment might work differently actually. The video also shows that a good Mercedes ICV should close around 1 amp and old, dirty ones require higher amperage. I guess the same / similar would hold true for the BMW one? I will check that and I will also try the adjustment one more time. I haven't let the engine warm up with the new ICV because of the very high idle.

A specific replacement for my ICV is still not available anywhere. Any other ideas what I can test?

[Aldo525]

 

 

I found and bought this ICV (eBay) made for W126 V8. It was the only 2-pin "L-shaped" one I could source. I tired it out but no luck so far. With it installed the idle is very high even when cold. I guess it might let more air through because it is made for a higher displacement engine? I tried the adjustment screw but it did not change anything. However I have found this video: https://youtu.be/hbQcWBykjbc?si=FPGkK9aoh7jsbdt4 and I think I the adjustment might work differently actually. The video also shows that a good Mercedes ICV should close around 1 amp and old, dirty ones require higher amperage. I guess the same / similar would hold true for the BMW one? I will check that and I will also try the adjustment one more time. I haven't let the engine warm up with the new ICV because of the very high idle.

A specific replacement for my ICV is still not available anywhere. Any other ideas what I can test?

 

 

 

 

I was thinking in this kind of adjustemet screw, can't see the same in the ICV you bought. This screw limits the internal rotary movement of the ICV and thus limits the air passage. Also note that it has a diameter reducer at the inlet, perhaps it is an option to study with your new ICV.

[teh]

I am a bit hesitant to say so, but I think I might have fixed the issue today. 

I had the ICV on the bench doing some measurements and came across an older post where someone said, with the ICV receiving power and in the closed position, when you blow through almost all the air should get blocked. Mine however let through a lot of the air. 

I could not figure out why and decided to play around with the adjustment screw again. With the screw in the full "screwed in" position, the airflow started to be really restricted with the ICV closed. 

I put the ICV back into the car and did a test drive. The idle is considerable lower at any engine temperature and so far no surging idle. Sitting at a red light never felt so relaxed before in this car . I really really hope this issue is dealt with now, I was starting to get really frustrated about this issue and the constant surging idle.

I tried to adjust the screw before with the car idling but could not see any change. However I had read that the adjustment is quite sensitive so I never went to the full screwed in position. I suspect the adjustment had been messed with by the previous owner/mechanic to "deal with" vacuum leaks or something like that. I don't know if the ICV adjustment screw is now at the "correct" position but at the moment I don't really care since it finally is some progress. 

A few words on the video I posted about the Mercedes ICV:

According to the author of the video, ICVs for the 560 and other V8 Mercedes engines should close at around 1 amp and dirty or old ones need more amps to close. I measured the aftermarket Mercedes unit I bought and indeed it closes right at 1 amp. 

The ICV out of my 525e closes at 0.5 amp already. The Mercedes on is not closed at 0.5 amp making me conclude that the Mercedes one sadly is not a possible alternative. I don't have any factory numbers for the BMW unit so take it with a grain of salt but based on the fact that old, dirty units should require higher amperage, I am assuming mine is actually not that gummed up and 0.5 amp might be close to the factory number.

And a tip for anyone reading this at a later point while trying to diagnose an idling issue with this car:

Don't start with messing with the adjustment screw! Check all other points that I mentioned in my original post first. A vacuum leak for example is much more likely. I double checked that today again to rule it out once again.