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Old 03-28-2017, 04:09 AM   #1
ElmoPerkins
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Default AFM or not to AFM. That is the question.

Hey all. If you saw my knock sensor and under the intake project, then you will know kinda what's going on.

I've got a cold start idle issue as well as an all around idle problem at all temps for that matter. The engine rpms are way too low and the engine will stall. Cold starts it fires after 1 to 2 seconds, then stalls unless I have my foot on the gas to keep the revs up. Same once at operating temp when rolling to a stop or sitting stationary.

I know the AFM has been tweaked by having the spring adjusted to smooth out the engine. This was pre vacuum leaks. Now that everything is sealed up tight, I have to make some AFM spring adjustments.

Also 1st time after finishing my project, I ran the car with the icv unplugged. It was the only way to keep the revs up without manually adjusting the throttle cables to keep the t body cracked open. With accessories on (a/c, rear defrost and lights) everything seems ok besides the cel for the icv. Power delivery was smooth all the way to redline, something I was trying to fix from the get go. It would bog down at WOT or seem to be struggling to give 100% power. 3/4 throttle would be max power if that makes sense with no hesitation or flat spot in the power band.

Today I plugged in the icv and made some adjustment to both the throttle cables and the spring in the AFM to keep the engine at a stable idle rpm of 800 ish. Every time the icv was connected, the engine rpms would drop severely and stall unless throttle was induced to keep it from stalling.

Now the idle seems to be at 800 rpm with no accessories on. I can add one load at a time and watch the rpms drop slightly. Once a/c, rear defrost and lights are on, the idle is down to 400 rpm and eventually stalls.

It's like the icv is not adjusting to keep the engine rpms at the target idle rpm. Like when it's plugged in. It goes to full closed which is a very small gap for air to travel through.

Also the flat spot in the power band is back in WOT situations.

At this point, I am unsure as to replace the AFM with a used oem one off eBay, shell out a lot of money for a new genuine AFM, or go reman from rock auto. OR convert to MAF, which from what i read is not very feasible if the car remains stock, which it will.

I have read out the status requests with ISTA and air flow is in spec at idle and the intake air temps are reading correctly.

Does anyone have any input on this? I really don't want to throw expensive parts at it and after all the repairs I did, I figured this thing would be running top notch. I feel like I'm at a loss ATM and not sure where to go from here.

Thanks for the help!
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Old 03-29-2017, 01:54 AM   #2
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If disconnecting the ICV makes the engine run better, then that makes the ICV the prime suspect, doesn't it?
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Old 03-29-2017, 02:23 AM   #3
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Well, I think there is more to it. Now that I have the icv plugged in and the engine is idling 800-1000 rpm, I can disconnect it and the revs go up. Sprung open allowing more air to enter. I bench tested the icv when everything was apart. I applied 12v and saw movement/closing, took power away and springs open. My next step is to check the signal from the dme to the icv with an oscilloscope. From what I understand, this signal should be a pulse width modulated signal controlling how far the icv is closed.

It sounds at the moment as if it is 100% activated while plugged in regardless of load, temp, etc.

Also knowing the AFM is not factory set makes thing that much more difficult to identify the problem(s). I don't have a spare icv or afm to swap and test so I'm kinda stuck.

Also I need to read up on the throttle cable adjustments. I assume they just need the slack taken out of them so the throttle has no slop. Any more adjustment and then rpms will change and the engine is slow to return back to idle rpm.
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Old 03-31-2017, 10:15 PM   #4
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Brand spanking new Genuine BMW AFM ready to be installed. I'll let y'all know how it goes!
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Old 04-01-2017, 01:31 AM   #5
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Welp. Looks like I still got more problems then just an AFM. Still starts up then stalls. Have to apply some throttle for it to finally start and run. Let go of the throttle and stalls. It also seems to hesitate a bit when "blipping" the throttle but it was cold so, yeah.

It also smells pig rich too. Maybe why it hesitates when "blipping" the throttle. Might just be a cold start/open loop deal. The rich fuel smell seems to diminish once warmed up.

I then proceeded to unplug the ICV again and immediately the idle raises up to about 1000-1100 rpm and the engine stays happy. Check engine light comes on for the ICV of course but sounds as if the next thing to try is the ICV.

I am curious though if anyone has had a bad dme trying to fix this issue? Like the output signals from the dme to the ICV become corrupt?

Anyone please chime in on this and let me know what you think.

Thank you.
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Old 04-10-2017, 02:44 AM   #6
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It seems to me the ICV is the culprit. Can you pull a used one at a bone yard to test?

The beauty of electric components is they are expensive and cannot be returned once opened.

As far as corrupt output signals: I suppose that is possible but a DME is not an iMac. It's pretty simple and generally either works or doesn't. I was involved in one swap where the car owner ended up with three bad DMEs but they just didn't work. I've never seen all well but one output signal.
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Old 04-10-2017, 03:09 AM   #7
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Quote:
Originally Posted by J!m View Post
It seems to me the ICV is the culprit. Can you pull a used one at a bone yard to test?

The beauty of electric components is they are expensive and cannot be returned once opened.

As far as corrupt output signals: I suppose that is possible but a DME is not an iMac. It's pretty simple and generally either works or doesn't. I was involved in one swap where the car owner ended up with three bad DMEs but they just didn't work. I've never seen all well but one output signal.


Thanks for the input! I don't have access to a known good ICV and hesitant to get a used oem one on eBay or a China knock off.

I haven't have time to scope the output signal yet so I've been driving it with the ICV unplugged. The rpms get up fairly high 1400-1500 when warm and sitting at a traffic light. The engine will also start bouncing rpm from 1500-1100 like the dme knows it's idle is too high and cuts fuel to lower the rpm. I usually call this "DSM"ing because of the old 1st gen eclipses would have bouncy idles at times. Lol!



This is what I'll be testing.
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Old 04-10-2017, 02:18 PM   #8
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Those old Eclipses were usually needing a MAP sensor in that case... My old Daytona had the same issue.

I see what you have there in the ETM but that document does not tell you what that signal is supposed to be... It may be variable voltage from the DME as it appears to operate a coil (if the diagram is to be believed) like in a relay. It is also possible there are internal components that regulate voltage flow to that coil based on temperature in the valve itself, since it seems to have no other connections...

Does the valve only have two wires going to it, or more? If more, you need to find those in the ETM and determine their function.
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Old 04-10-2017, 02:26 PM   #9
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It only has 2 wires and I assume it was a pulse width modulated signal from the dme. Pin 29 at dme is the ICV control, then goes to a ground point, then to pin 54 which I assume is dme ground.
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Old 04-10-2017, 02:56 PM   #10
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Maybe you already realize this, but often the pin out is scattered throughout the diagram. One of the things I hate about them, but it is what it is...

When you disconnect the actual valve connector, does the connector have only two wires in it? If so, I'd say you are absolutely right with your assumptions. And those are your wires.

However, if it has a third (or more) wires going to it, you have to search throughout the document for those wires, and where they go. They may not even go back to the DME just because BMW like to keep it interesting.

It also looks like you have an actual dealer bound book there... Or did you print off the soft version? And finally, is the version of the ETM you have the right one for your car? I have noticed that even within a model year, there can be "early" and "late" model production variants. Not trying to make it worse for you, just making sure you've covered your bases.
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Old 04-10-2017, 03:04 PM   #11
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I can confirm it's only a 2 pin connector for the ICV.

I work at bmw so i have access to the "library of old school ETM books" lol! The book I was looking at was for 1995 E36 all models. The 318ti only book I found was for 1997.

I hear you on the early and late model production diagrams. Im 99% sure the pages I took pics of are what I got on the car. As u said, bmw keeps it interesting.
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Old 04-10-2017, 03:21 PM   #12
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OK So what exactly are you working on? A 1995 318ti? I think we have links to the ti diagrams here at the 'org. It may be worth your while to double check that.

I can confirm the ti is different that a 318i of the same vintage. And the only year "worse" than 1995 for the ti was 1996 due to the crossover from OBD-I to OBD-II. I've had the worst luck dealing with 1996 models.
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Old 04-10-2017, 03:28 PM   #13
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Yeah 95 318ti with the m42b18. Production date is 11/95. So obd1 yay!

Thanks for your help J!m. I will double check the diagrams before I test the icv.
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Old 04-10-2017, 04:50 PM   #14
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Yeah, see if we have the 1995 ti diagram. We should. Just double-check.
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