High warm idle on E21

[cchase]

Our 1982 BMW 320i has a recent habit of idling at about 1400 rpm when warm. It should be 850 +/- 50 rpm.

I'm not exactly sure where to start diagnosing this. I don't believe there are any vacuum leaks, I'm getting 14" of steady vacuum at idle and the engine is operating properly. Valves are properly adjusted, timing is good, and the stuff that would immediately come to mind (such as the idle speed screw) has never been messed with, so I don't know why it would change.

Any ideas from anyone here as to where to start looking? On a hunch I did play around with the cold fuel injector and the auxiliary air valve but it would appear neither are the culprit - pinching the aux. air valve line doesn't change idle speed, nor does unplugging the injector.

Hoping someone on here has some experience with these old M10 mechanical injection units.

 

[simple_gifts]

I need to get out more; thought this was a thread on ethanol.

 

[mene]

Ohhh the Bosch K-jectronic!. OK, I haven't touch one in over 16 years but let me take a crack at it, I still have the manuals to repair them just have to look if you want me to. OK the "idle speed screw": is "not" such thing, it is a stop screw for the butterfly not to jam itself into the throttle body so it is not to be touched ever unless you take the valve apart and have to re-set it, the idle is controlled by the air valve, you mentioned that you pinch the hose and doesn't budge, it sounds like a leak since that is actually the upper limit of control of the valve, so it is either stuck open (pretty common IIRC) or has another leak somewhere else, PCV? brake booster check valve?. Please keep us informed.

 

[cchase]

Interesting. The idle screw adjustment I got from the factory repair manual. It tells you to adjust the idle to 850 rpm by turning the screw (and has some obscure picture showing where it is, although I didn't immediately see it). So you are saying there is no such screw? There is also a video on Youtube showing how to adjust the fuel trim and they alternate between adjusting the fuel trim and then adjusting the idle speed...

The diagram I have for the air valve shows it basically bypassing the throttle body when the engine is cold, and shutting when warm. Thus, I thought that by pinching it when warm, I could check to confirm that it was closed, since if it was open, pinching would simulate a closed condition. Is this wrong? This is where I was reading about the air valve: Bimmerforums - Aux air valve adjustment made easy!

 

[mene]

I'll tell you what, if you are not in a hurry I'll look for those manuals, are the specific for K-Jectronic and give them a look over and if you haven't found a solution I'll tell you what I found. Does that sound good to you?

 

[cchase]

I'd like to fix this the right way. So any help or ideas is greatly appreciated

.

 

[mene]

Also, from that link, what they call A/C compensation valve I remember it as the air control valve, in charge of idle all the time, yes it does open more when the A/C is on but also when the lights are on too or any other load but.... let me double check I could be confused with the L-Jectronic.

 

[cchase]

The car doesn't have A/C but I assume the function is the same regardless. It sounds like you are saying that perhaps it is only load based though, not temperature based?

 

[mene]

No, again IIRC there were two valves, one for the cold idle and the other for the hot idle since the latter didn't have enough range. Let me double check.

 

[mene]

OK! I found the Bosch injection manual but not the specific for your 320/E21. This is the deal, there is an idle control screw at the throttle valve usually has a knob but not always;you can have an "idle speed stabilizer" valve which will control the idle all the time based on load and engine temperature, or you can have an "auxiliary air valve" which is a crude hole that opens up inside the valve when it is really cold, around freezing mostly, the former is handled by an electronic controller and the latter by an engine temperature sensor. I could not see much of the air intake in the cylinder head image in the other thread but I did see a temperatue sensor not well plugged, that is enough for the idle speed stabilizer to think the engine is cold and open up the bypass to keep the RPM high. Can you take an image of the induction system? I might be able to recognize either of the valves but no promises. By the way don't touch the idle speed screw until last resort and a throttle stop screw does exist as I remembered and it is not to be touched.

 

[cchase]

I do think I saw the throttle stop screw, next to the timing vacuum advance line, or in that area. Wasn't going to mess with that.

As far as the temperature sensor not plugged, no one seems to remember back far enough but there are actually 2 unused plugs that were replaced by 2 other plugs. I don't know the exact details as to why but the plug you can see in that picture has been disconnected for nearly forever.

As far as pictures, I will take a few tomorrow in the light.

 

[mene]

That is odd, Was it working well with the plugs disconnected?, In the link you posted you can see that the 528 engine has both valves, they are calling the air speed stabilizer valve a/c compensation valve or something like it, and again yes it does give more air to the engine when the A/C is on but also when everything else that loads the engine is on too.

 

[cchase]

It's not that the plugs are disconnected. Somehow they were replaced with other plugs and just left there. Long story short, the temperature sensor does have a plug on it.

 

[JHZR2]

Is there an icv??

Mine is the opposite, it won't fast idle even in extreme cold. Doesn't misfire or have any ill effects, but it is supposed to... The most notable thing is a bit of an RPM dip when AC engages, indicating that something is lazy. I'd start with an analysis of the icv and its circuit.

 

[cchase]

I think what you're referring to as the idle control valve (ICV, right?) is what I am referring to as the auxiliary air valve. It's the only thing I can find that bypasses the throttle plate and would assume that function.

Does anyone know what the vacuum at idle should be on these engines? 14" sounds low to me since all my other vehicles are closer to 22" at idle but I'm not sure and none of my manuals have a specification for it.

 

[waltb]

I have had a few E21 BMWs. High warm idle is usually caused by a vacuum leak somewhere. These engines are extremely sensitive to air leaks. It could be a cracked PCV hose, cracked air flow meter rubber cover, cracked vacuum line, cracked hoses to and from the aux air value, old injector O-ring seals, or a dipstick not sealing well.

It can also be a stuck open aux air valve which can be mechanically stuck open or it could have lost its power to the little heater inside of it due to old or corroded wiring (happened to me). You can test the aux air valve by heating it up and the little slot in it should close up.

In the older E21s, a high idle can be caused by the vacuum retard vacuum valve sticking closed (it was a disk shaped think mounted to the manifold) but I don't think the '82s had any vacuum retard.

I would recommend finding one of the E21 digests/forums elsewhere on the internet and asking the question.

WB

 

[cchase]

Are you saying to test the aux. air valve by heating it up while its connected? Does it require power to work or is it just some kind of element in there? I'm not sure whether the plug is providing power or reading some kind of status, in other words.

We did take the valve assembly off this morning and the little slot opens and closes freely, but I suppose if whatever is supposed to make it move, isn't moving, it doesn't matter whether it moves freely or not.

I don't think there are any vacuum leaks but I still am not sure how much vacuum it should be pulling at idle. None of the hoses are cracked or missing.

It is definitely sensitive to vacuum leaks though, since unhooking any vacuum line immediately causes the engine to stumble and die.

 

[mene]

The aux. air valve (the one for cold start only) has a heating element (resistor) inside operated by 12v. it heats a bimetalic spring that turns the disc with the hole to mis-align it if you will with the in and out fitings so it doesn't let extra air go through lowering the idle, I hope is understandable the way I explained, all this is switched by a cold temp. sensor in the water jacket; so if you heat it externally you will be simulating the internal heating provided by the resistor, that is one way to test it, but you mention that you kinked the hose with the engine running and did nothing and that is the best quick test to check if the problem is there or not and obviously is not unless the hoses are leaking. Did you have a chance to take a picture of the induction?

 

[cchase]

I didn't have a chance to actually get out there with the camera (the car is covered and tucked away in the garage).

I do have some pictures from a few years ago though of the top of the engine area, so here they are for now:

 

[mene]

There is your problem.... you need to throw some dirt and mud over that engine bay, you took away whatever was plugging the leak!. Just joking, you should take that car to the dealer and show them how a new car should come out of their lot. I can't see the idle stabilizer valve it probably doesn't have it, 1400 RPM is a sizable leak if it were to atmosphere you should be able to hear it, just thinking out loud, it is running fine Right?, no hesitation or lean running, no slight misfire in cyl. 3 either, I gather; Is the throttle cable returning fully to it's end? asking because it seems that the air leaking in is passing through the metering valve (the disc that goes up and down at the fuel distributor unit) otherwise it will run lean, the system is actually measuring that extra air unless the cold start system think is around freezing and is not heating the aux. valve and energizing the cold start injector too keeping the mixture somewhat correct or even richer but then again we come back to you pinching that hose and nothing happening. Floor mat not letting the pedal to fully return like a Toyota?