AFM Tweaking/Calibrating - Ideas?

[TheWolfman]

After much 'dicking about' (technical term) trying to resolve my high-idle (about 1300) in my pre-facelift 320i I am slowly starting to look at the Air Flow Meter as being a point of serious investigation.

I came across a really good video with a wealth of information on the subject of refurbishing the AFM here:

https://www.youtube.com/watch?v=Z-QlPtsjh7g&t=111s

What I found particularly interesting was a very good point mentioned about how our older Beemers were calibrated to use very different fuel to what we're putting in them today and subsequently need to be tweeked somewhat in order to compensate for modern fuel types.

It also got me thinking about how adjusting the mix via manually mechanically altering the cog in the AFM can be done to alter the mix, then it might be possible if the electrical voltage lowers to just achieve the same thing by putting some resistors in series with the AFM output to bring the values closer to what they would be if it was manually adjusted.

I'm starting to think that this is at the heart of my issue and will hopefully begin to investigate this soon.If anyone has any experience or ideas on this subject and they would like to share them that would be great.

[MunsterScot]

You're link only re-opens this page and not you tube (at least it does for me).

Have you had a read of this:

http://bmwe30network.net/forums/read.php?3,9615

Might help.

[TheWolfman]

Thanks Munster, yes I've already read that one, very handy article though.I've corrected the link, so now it opens the correct video, pretty concise information alongside this rather good post on a V-Dub Bus forum of all places!:

https://itinerant-air-cooled.com//viewtopic.php?t=7761

Explains it all very clearly without too much unnecessary guff.... If however guffs your thing though and you want to get even deeper into it all I found this rather 'extensive' post on the subject here:

http://www.k100-forum.com/t11055-bosch- ... on-summary .

[stones]

It is generally not a good idea to mess with the AFM unless you have gone through the entire engine to check for any air leaks even the smallest split in a pipe can affect idle. (Also manifold and throttle body gaskets)
Also fuel injectors not working correctly, blue temp sensor not reading correctly.
If all checks out then you should use a exhaust gas analyser whilst adjusting the AFM.
HTH

[paultv]

One thing no one has mentioned is the throttle stop screw. Some owners think this sets the idle, nope it simply stops the butterfly from closing too much and jamming in the throttle body. Check if the set screw has been messed with it should be sealed with red paint but most cars this age have been wrongly adjusted at some point.

Just a thought

Paul

[TheWolfman]

Ahhh yes, the fabled throttle stop screw.I actually got around to that one not too long ago. Someone had wound it all the way out and thus the TPS wasn't reacting correctly, once I set it correctly so it just touches the stop, the whole throttle response was actually massively improved in the low end.

[Brianmoooore]

What I found particularly interesting was a very good point mentioned about how our older Beemers were calibrated to use very different fuel to what we're putting in them today and subsequently need to be tweeked somewhat in order to compensate for modern fuel types.

NOTHING has changed in the relationship between modern fuels and the AFM! Optimum air/fuel ratio for both max. power and max. economy is exactly the same now as it was then.
AFM signal isn't used at idle*, and it makes no difference if you unplug the AFM when at idle (not quite true in practice, because you will be unplugging the inlet air temp. sensor at the same time).
* a faulty AFM can send out a signal so that the ECU thinks the engine is not at idle.
If an engine is turning at 1300 RPM, it must be getting enough air to let it do so. It can only get this air from a) the gap past the closed throttle butterfly, b) the bore of the idle control valve, or c) an air leak on the engine side of the throttle body.

[TheWolfman]

Thankyou for the clarification Brian,AKA The Zone Don! Also thankyou muchly for publicly revealing my clear stupidity on the matter at hand..

I am certain that the issue can only now then lie with an undiagnosed air leak due to the following:

• The Throttle and TPS is now entirely within spec and working correctly

• The ICV (Actually Water Slide valve as it's a 320i L-Jetronic) is working within spec

• The Throttle Stop Screw is set correctly

• AFM IDLE valve is set to factory spec

The engine sometimes needs to turn over a fair bit to start, but sometimes starts straight away....which makes me think that it's sometimes flooding because it's getting incorrect data from AFM, either that or there is some fuel pump/injector issue.

The main symptom is that when the car starts it starts at about 1200-1300 RPM then over 10-15 seconds or so surges up to about 3000 RPM when in 'Park', this must be happening as vacuum is created which would also suggest an intake leak maybe? The Revs drop to about 1300 when any gear is engaged, but stays at about 3000 when in 'Park',When the engine has warmed up however the revs when in ' Park' settle down to about 1300 the same as when idle in-gear. I'm guessing this has to do with the 'Air Slide Valve/Water Slide Valve' closing when warm meaning it's operating correctly.

I did find that tweaking the AFM did solve the vehicle running somewhat rich and has improved fuel economy somewhat.One thing I could recomend NOT doing however is adjusting the height of the copper arm on the spindle in order to get the copper arm to run on some fresh carbon track.. this resulted in the motor not starting, which I'm assuming was down to the AFM output now being non-existent or incorrect.

Let the adventure continue!....


***

"First, a little piece of basics. Due to the nature of things there's an air-fuel ratio that is supposed to be correct for total combustion. This is the 14.7:1 air:fuel ratio. Of course it isn't the best for either power or mpg. It is usual to refer to certain lambda values, i.e., 14.7:1 corresponds to lambda=1 and (14.7*0.9):1 is lambda=0.9. For the best power lambda=0.88 is feasible and lambda=1.1 for mpg."

***

[paultv]

Wow, didn't realise the revs were so high!!

from the Wiki:

The air slide valve is a water-controlled valve located under the inlet manifold. Fed by two coolant pipes and two air pipes, it is meant to open when cold, and close when fully warmed up. The idea is to regulate the different air requirements of a cold and a hot engine when idling.

Because it is based around a sliding mechanism, it is not uncommon for the slide valve to become sticky over time, or to lock up completely. If this happens, your cold idle will suffer terribly although your warm idle will still be acceptable.

To test the air slide valve, clamp the long hose that comes across the inlet manifold to the idle bypass screw housing when the engine is hot. If the revs drop when you clamp the pipe, the valve is faulty. You can attempt to remove, clean and refit the component, but most often the unit will need replacing, as they are not repairable

Paul

[Speedtouch]

I agree with Paul above. I had a 1987 320i pre-facelift with the same high idle problem - turned out to be a stuck air-slide valve. Very common problem on L-Jet cars. You can try freeing it off with penetrating fluid, but usually replacement is the only cure.

[TheWolfman]

Thanks for the info guys,although I must say I'm pretty familiar with the little so-and-so that is the 'Air Slide Valve' and posted some extensive information on it on the Zone in the following thread:

viewtopic.php?f=2&t=278104&hilit=air+sl ... lide+valve

As the Air Slide Valve's default position when at cold idle is actually 'open' in order to provide extra air and 'closed' when the engine is warmed up it is functioning as intended as the rev's drop when the engine is warm. I have two Air Slide Valves which both function correctly and there is no difference when either is installed.

[TheWolfman]

I thought I'd post a little video of the issue at hand in the hope that someone might be able to shed some light on it...



In the video you can see it's one of the moments where it has trouble starting straight away and when it actually starts you see the rev's rise up to about 3000, when the rev's then drop that is me changing gear out of 'park' and into 'drive' where it sits at about 1600

This is from a cold start.When starting warm you don't get the surge to 3000 and it sits at about 1200 in Gear and slightly higher in Park. This indicates that the Air Slide Valve is doing what it's meant to do but the idle is still high.

I have this evening constructed a pretty crude but effective smoke machine and will be endeavouring on doing a smoke vacuum leak test tommorw... lets see what happens eh?!Wish me luck!

[TheWolfman]

Also took the sparks plugs out to check for any tell-tale signs, but I can't really diagnose a lot from these and they look ok to me....but I'm certainly no expert:

[TheWolfman]

So I've spent the day getting my smoke on!.....I was expecting for it to be a case of 'find where it's not leaking' rather than 'find the leak' but as it turns out it seems that the whole vacuum system is kosher apart from a leak on the breather hose to the rocker cover:

Check the video:



The offending little piece of pipe.The underside which you couldc't see was completly wrecked and the previous owner had just tried to tape it up... :

Here's the crude smoke machine I banged together utilising a cheapo Screwfix Soldering Iron and and the biggest jar of olives I could find.A lot of olives were harmed in the making of this device.

The "smoker" connected to intake via a rubber glove:

After having the Eureka! moment and discovering this leak I thought all my idle issues would be solved, but alas that is not the case.After sorting the leak I have managed to get rid of the surge somewhat, but the engine STILL idles high.I really think the AFM is the culprit and am going to have a tinker with it tommorow.

One thing that does seem to be the case is that once I adjust the AFM to bring the car down to the 800-1000 Idle range the engine idles very roughly, bucks quite a lot and also get a little black smoke out the back end..not good.If you've seen my other thread on spark plugs,I'm now thinking that maybe the plugs are causing this roughness when the engine is actually in the correct idle range maybe? ONWARDS!

[Foe]

Hats off to you sir
As for the smoke machine....iginuity at its finest, even at the sacrifice of olives!

[TheWolfman]

ha!Thankyou...

Ya know what they say, you can't make an omelette without breakingg a few eggs....and you can't make a smoker machine without smashing a few olives! I couldn't get this out of my head the whole time I was making the thing...



Still would like to sort the bloody idle out though.....that would be NICE.

[Foe]

And good luck with getting to the bottom of your idle issue!!

[TheWolfman]

Thanks man

[TheWolfman]

After spending yet another day under the bonnet the Idle issue remains.I have however retested the AFM Temperature Sensor and I think it's banjaxed.... according to the Bently manual it should read around 2200-2700 Ohms across pins 8 and 9 on the AFM. It reads about 170 Ohms, so fair to say well out of spec! Looks like a new (old) AFM is on the cards.Would the Air Temp sensor really throw the idle off that much though?I'm unsure about this but maybe someone else is more informed than me about it...

Things I am now 100% certain of:

• TPS is in spec and operating correctly, tested with Meter and Clicks as it should

• Throttle Body is Clean and operates smoothly

• Throttle Cable is adjusted correctly as is the Stop Screw allowing the Throttle to close to TPS 'click' position

• Smoke tested intake multiple times, no Vacuum leaks are present

• Idle Valve/Additonal Air Slide Valve/Water Slide Valve...whatever you want to bloody call the daaaamn thing is operating correctly

• AFM Idle bypass valve set to factory spec

On a side note, fitted new sparks and fitted NGK ZGR5A's which have a deeper spark to the Zone recommended NGK BP6ES.These have certainly made the engine run more smoothly,and quietly, rockers seem softened, power seems good.

[TheWolfman]

If anyone can chime in with any possible avenues of investigation then that would be appreciated, looking at you here Mr Brianmoooore and Mr Paul TV!

I’ve also tested the Coolant Temperature Sensor, both at the sensor itself and at it’s respective input on the Engine Management System and this all checks out within spec.

Things I'm now considering:

• Dizzy and Rotorcap - Although I think this is a long-shot as their don't seem to be any timing/firing issues, well as far as I can tell at least

• AFM - Appears to be a faulty Air Temp Sensor in AFM as it is not within spec measurements.Not sure how much this would affect idle speed though?

Other than that I’m actually kind of stumped..

[bmw335icoupe]

I had a high idle on my pre facelift 320i convertible.

After a lot of digging it turned out to be low coolant level.
Once I topped up the coolant the idle was perfect regardless of the air or engine temperature
I could not believe it was so simple

[Speedtouch]

Not sure if you ever got to the bottom of your idle problem, but a common issue with pre-facelift L-Jetronic M20s is the water heated air slide valve, which often seizes and causes a high idle.

Sometimes, it can be freed off but most need replacing.