Idle Speed Air/Control/Slide Valve Confidence Check

[SMinn560sl]

For what it's worth, I've been fighting a slightly high idle on my car for quite some time now. Mine not only idles a little high, but surges around 1500 RPM and stumbles slightly at idle. General prognosis has been an air leak somewhere. I've taken the intake off so many times now that I think I can almost do it blindfolded (well, not quite).

After working on it myself for months without success, I took it to a Bosch fuel injection expert. He sealed all of the holes in the intake manifold and used a smoke generator to pump smoke under pressure to detect any leaks. He reported back that the manifold was leaking underneath, in the area of the rubber seals between the manifold halves, so I took the car home, removed the manifold, and replaced the seals. Incidentally, I previously replaced the idle control valve, the control module, injectors, and all rubber parts in the idle system and manifold in general (including the boot between the fuel distributor and throttle and all injector seals).

When all was back together, it ran the same. I subsequently took the car back to my Bosch expert, he smoked it again, and again proclaimed a leak under the manifold. This time I authorized him to repair the leak. He again replaced the rubber seals between the intake halves and again replaced the injector seals. The car is now a lot better, but still idles a little high and surges around 1500 RPM.

I'm convinced that I still have an air leak somewhere and plan to go through the idle control system thoroughly when I get another weekend at home. Of course, I guess it could also be the idle control valve not completely closing or allowing a varying amount of air to enter the system as it gets around 1500. I just don't know.

By the way, I'm not certain, but I do not believe my idle control valve has a screw adjustment as the pictures above indicate, but I'll check the next time I'm under the hood.

Edit: Curiosity was killing me. I just went out and pulled the hose off the back of the valve and verified that I do not have any adjustment on the back of my idle control valve. My car is an 86 560SL.

[BabyBlueBenz]

SMinn560sl, you're discouraging me.

If you've done all that effort and still have the same problem, then I may just settle for my current 1000 rpm warm idle.

Honestly, I didn't pay attention when I bought my car a few years ago and note how it idled back then. It definitely got worse a few months ago, easily reaching 1500 by itself (no stumbling though). With the Throttle Valve Switch recently replaced, the engine sounds "normal" to me.

Armed with Strife and other's suggestions to date, I have a few more things to check (alternator output, OVP, Oxygen sensor, temp sensor) before I give up on this task for now and move on the next item of concern for me...timing chain & guides health.

BTW, both my old and new Idle Speed Air Valve's were VDO brand and had the same threaded insert as dpetryk's photo. Here's a picture of my dissected ISAV showing the inside of the business-end:

[SMinn560sl]

Thanks for the picture B3. I have to admit that I didn't read the description of the adjustment fully and was looking for a screw protruding from the back of the valve (yeah, I know...). I'm off this weekend, so will give the screw trick a try. I'd expect the thread to be a standard metric thread instead of an SAE thread, but I'll try the size recommended.

Incidentally, if anyone is interested in building a smoke generator, it's really pretty simple. My Bosch guy's tester was just a can with a twist off cap like the type that paint thinner comes in. Essentially he had mounted a diesel glow plug toward the bottom of the can as well as an air hose fitting (quick release) into the top. As I recall, he soldered a small metal tube into the cap after drilling a hole in it.

To prepare it, he filled it up past the glow plug with hydraulic fluid (brake fluid), connected an air hose from his compressor to the hose fitting and slid a length of fuel line over the spout that he soldered into the cap. He attached two leads from a 12V battery to the glow plug and the can began pumping smoke under pressure from the compressor. He slid the free end of the length of fuel line over one of the vacuum nipples on the manifold and the system pumped smoke into the manifold. If you've disconnected all of the other pipes and hoses that feed the manifold, any smoke that escapes is a leak.

[rgp717]

Not to be the dope here, and I have a 85 380SL, which looks similar, but how (1) do you disassemble the Air Valve, and (2) make an "adjustment"? I too am in high idle hell.

[dpetryk]

IAC valve needs to removed from the car. 1 electrical plug and 2 hose connections.

Look at the picture in post #18. Find that spot on your valve. Its one of the hose connections. Remove a plug that covers the threads inside the valve. Insert the screw as shown in post #18. Pull the screw and brass piece out a SMALL - repeat - SMALL amount. The brass piece is press fit into the aluminum and some force is necessary to move it. I used a small prying device (screwdriver) under the nut to move it out. I use a vise to move it in.

Re install and test. Your idle should be lower. If not low enough repeat the process. If your idle is too low - go the other way.

[mbboy]

Originally Posted by dpetryk

Here is the adjustment. - You move it inward to increase the idle speed and pull it out to reduce the idle speed. When moving it make small movements. I use a flat tip screwdriver to pry between the nut and the housing to pull it out. I use a vise to push it in. The screw is a 10-32. It is not the right thread but it will hold. I do not screw it too tight for fear of trashing the threads inside the brass thing in the valve. I just make it hand tight but be sure it is seated. I could not find the proper screw to fit it. The 10-32 works great for me. Remember just small adjustments.

I was going to try this to reduce my high idle, since I've tried everything else, including changing the ICU, checking for vacuum leaks, adjusting the linkage, etc.
However, I assumed that the rubber ring this screw goes into was empty and threaded, but it isn't. The ring has a little brass cap in it. So, before I ruin my ICV, I was wondering if you change the idle by using this screw to push the brass cap down?

Thanks very much for any help anyone can give me on this procedure.

[dpetryk]

The screw is threaded into a brass piece which is threaded. Its not a rubber ring as you said. It may look like rubber in this photo but it is not. The brass part slides inside the aluminum part inside the 3 spokes you see in the photo.

Maybe your ICV is different than the one pictures here.

[dpetryk]

IIRC there was some sort of cap over the hole. Remove it and see what you have underneath.

[mbboy]

Originally Posted by dpetryk

The screw is threaded into a brass piece which is threaded. Its not a rubber ring as you said. It may look like rubber in this photo but it is not. The brass part slides inside the aluminum part inside the 3 spokes you see in the photo.

Maybe your ICV is different than the one pictures here.

Thanks for getting back to me Dave. Attached is a picture of an ICV that looks like the one that's on my 1981 380sl, as well as the one you showed. The part # is 0001411225, and it's used on the 107's with 116 960-963 engines, as well as the 117's with the 116 963.

As you can see, there's a little brass plug at the bottom of the inner ring, which looked to me like it was not threaded and made of rubber. I'm going to take it off again later just to make sure and, hopefully, after you've responded to this message.

Assuming that it is unthreaded rubber, however, do you think I could still use your technique to adjust my idle, assuming that the screw is going to hit that little brass plug? Or, do you think there might be another way to pull the ring out?

Now, I did notice that there's another ICV on Ebay, part #0001411625 that superficially looks exactly like mine, but it's used on 116.964 and 965, and the 117 964-968. However, I haven't been able to tell from the pictures whether the ring on that one has is different from the ring on mine. But maybe that would account for the discrepancy I'm trying to resolve?

[dpetryk]

HArd to tell from the photo how its put together. I would toss out the possibility that the part that has the 3 spokes might move inside the aluminum part. So that entire assembly of the spoke part and everything attached to it moves. My type of valve is press fit so adjusting it takes a good grip on that brass piece. It may be that your type needs to move the entire center assembly including everything attached to it.

Just an idea.

[hookedon210s]

All good advice in this thread. On my 1983 380SE (euro) I had high idle problems for quite some time. Note that the early Euro ICV's are different than the US versions since there is no vacuum advance at idle on the early US cars so the US versions have to flow more air to idle at the correct speed. This difference presents an opportunity to use a Euro ICV to reduce airflow and hence the idle rate of a US engine. Also note that the absence of vacuum retard at idle due to vacuum retard can diaphragm leaks on the early US cars can cause a high idle. To continue, I cleaned/ replaced the ICV multiple times, replaced the control unit a couple of times with rebuilt, checked for vacuum leaks, etc. without totally resolving the issue. In desperation I finally bit the bullet and bought a new control unit from the dealer and solved the problem. My assumption is that the rebuilders generally do an incomplete job which leaves the current handling/pulsing abilities of the control unit below what is required to maintain the proper idle. Also note that the revision to the vacuum lines substitutes a solid (closed) vacuum line which reduces idle airflow slightly and will in turn reduce the current/pulsing requirements of the idle control system. Mark

[daimlerdude]

Originally Posted by dpetryk

HArd to tell from the photo how its put together. I would toss out the possibility that the part that has the 3 spokes might move inside the aluminum part. So that entire assembly of the spoke part and everything attached to it moves. My type of valve is press fit so adjusting it takes a good grip on that brass piece. It may be that your type needs to move the entire center assembly including everything attached to it.

Just an idea.

After taking a closer look at my valve, I can see that the ring I identified as rubber is indeed metal, and that the little brass piece in the center of the ring is in fact some type of cap.

However, that cap is recessed and, as far as I can tell, it's sitting in a spindle that connects the ICV's outer ring to the ICV's revolving wheel. So I can't figure out how to remove the cap, especially without risking having it drop down into the ICV?

I should also note that, per your instructions, I cleaned the ICV out, even more thoroughly than I had before with brake cleaner and an electronic component cleaner. But that didn't change the idle one bit. OTOH, I could see that the outer rim of the revolving wheel still had some caked on carbon on it, which I couldn't remove.

So, that's where I'm at right now

[daimlerdude]

Originally Posted by hookedon210s

Note that the early Euro ICV's are different than the US versions since there is no vacuum advance at idle on the early US cars so the US versions have to flow more air to idle at the correct speed. This difference presents an opportunity to use a Euro ICV to reduce airflow and hence the idle rate of a US engine. Also note that the absence of vacuum retard at idle due to vacuum retard can diaphragm leaks on the early US cars can cause a high idle. Mark

Mark,

Can you tell me which models you're referring to? When I access the engine/injection section of the 380sl European model on the EPC, it says "Not valid for this model. And, AFAIK, neither the 350sl nor the 450sl had an ICV.

BTW, the part # of my ICV is 0001411225.

Thanks in advance.

DD

[hookedon210s]

I just looked at the EPC to determine the ICV part numbers which are as follows:

380 and 500 USA: 0001411225
380 Euro: 0001411325
500 Euro: 0001411425
420 and 560 Euro and USA: 0001411625

IIRC the USA 380/500 ICV has a notch cut in the slide which will admit more air for a given pulse rate than the EURO ICV. The big block ICV's have a larger cross section and greater opening depth when at rest. It would seem that MB's goal was by tailoring the ICV sizes for each engine the idle computer would operate in the same range regardless of application. Please confirm this for yourself since it has been some time since I had to deal with this issue. Also I just checked prices on 380 USA and Euro valves and the prices are through the roof (discontinued/dealer only apparently). The other difference in the systems was the earlier 380/500's used the 16 deg. C oil temperature sensor to tell the computer the engine was cold and thus needed a higher idle rate and the later systems used a water temperature sensor. Mark

[daimlerdude]

Originally Posted by hookedon210s

I just looked at the EPC to determine the ICV part numbers which are as follows:

380 and 500 USA: 0001411225
380 Euro: 0001411325
500 Euro: 0001411425
420 and 560 Euro and USA: 0001411625

IIRC the USA 380/500 ICV has a notch cut in the slide which will admit more air for a given pulse rate than the EURO ICV. The big block ICV's have a larger cross section and greater opening depth when at rest. It would seem that MB's goal was by tailoring the ICV sizes for each engine the idle computer would operate in the same range regardless of application. Please confirm this for yourself since it has been some time since I had to deal with this issue. Also I just checked prices on 380 USA and Euro valves and the prices are through the roof (discontinued/dealer only apparently). The other difference in the systems was the earlier 380/500's used the 16 deg. C oil temperature sensor to tell the computer the engine was cold and thus needed a higher idle rate and the later systems used a water temperature sensor. Mark

Mark, thanks very much for researching this for me. The 0001411225 slide in my ICV does have a notch. So, if I read your right, you're saying that using a 0001411325, 0001411425 or 0001411625 will work in my 380 and could possibly lower the idle, because none of these have a notch.

Have you ever heard of anyone doing this, or are you speaking purely theoretically. That's not to say that there's anything wrong with theorizing. I'm just trying to calculate the risk-reward ratio of having one of these other units lower my idle. If you had to speculate with impunity, what would you say the odds are?

BTW, I'm not sure when this high idle thing began, but I did replace the oil temperature valve on my car fairly recently. However, if that was the problem, I assume that pulling the lead to the valve would cause the idle to go down, and it doesn't?