Hunting for idle when coasting, VSS related?

[trackjunkie21]

Excellent...well, not excellent, but we can build on this. :)

The engineer in me wants to know the facts! We can figure this out!

I timed mine 5 times between 8:45 and 9:00 until the O2 clicked on. Please check yours guys and see if your O2 does the same. You can verify this with a voltmeter wired into the GRN and BRN wires on the engine side of your O2 plug.

It will also help us all to know what we've replaced to try and fix the problem.
Here's a list of things I've tried to fix the problem:
-Replaced coolant sensor
-New MAF
-New O2 Sensor
-New relays (all 3)
-Wired up Fuel pump into fuse 11 (eliminated O2 backfeed)
-Wired up VSS to VDO cluster
-New Vanos Solenoid
-Replaced DME
-Checked fuel pressure at pump
-New coil packs

Here are the main components of my swap:
-S50 engine (modified internals)
-E36 harness
-VDO cluster
-'86 build 325 chassis
-506 Silver or -413 Red DME (with custom chip)

Nearly all components on my swap are new and I've checked more things than this, but the above replaced things I know without a doubt are good.

Well my m50 was basically fully refreshed inside and out, all new gaskets, o rings and such. So I know there are 0 vacuum leaks, I have replaced all sensors in the engine minus the IAT and the ICV, I already ordered a new ICV since I am pretty anal about electronics. I swapped DME's with known good ones as well as MAF's with no effects on the car's behavior. I have a chip in my 403 DME but the problem has been occuring before the chip was installed and it is a TRM off the shelf tune. I have an e36 wiring harness and a VDO cluster now which was swapped into my 1991 318i chassis. I will be checking the 02 sensor engagement tomorrow and also forgot to mention that when I replaced my 02 sensor, and I started the car up it threw my 02 heater code. I reset it and for about a week or so everytime I started the car up, my idle would be rather unsteady for a few minutes and then level out.

[Highway1]

Glad i found this thread. Mine does the Exact same thing.

[trackjunkie21]

Glad i found this thread. Mine does the Exact same thing.

specs on engine? It would be best for you to list them that way we can conclude as to what is NOT causing it so we don't end up throwing random parts at it.

[lolcantturn]

So thats what, FIVE people with the same problem including me?


Whoever finds the solution to the problem gets a personal blowjob from me.

[trackjunkie21]

So thats what, FIVE people with the same problem including me?


Whoever finds the solution to the problem gets a personal blowjob from me.

AAAAAAnd quoted.

[Beej '86 325es]

Well my m50 was basically fully refreshed inside and out, all new gaskets, o rings and such. So I know there are 0 vacuum leaks, I have replaced all sensors in the engine minus the IAT and the ICV, I already ordered a new ICV since I am pretty anal about electronics. I swapped DME's with known good ones as well as MAF's with no effects on the car's behavior. I have a chip in my 403 DME but the problem has been occuring before the chip was installed and it is a TRM off the shelf tune. I have an e36 wiring harness and a VDO cluster now which was swapped into my 1991 318i chassis. I will be checking the 02 sensor engagement tomorrow and also forgot to mention that when I replaced my 02 sensor, and I started the car up it threw my 02 heater code. I reset it and for about a week or so everytime I started the car up, my idle would be rather unsteady for a few minutes and then level out.

Translation... ;)

trackjunkie Items replaced:
-Replaced all sensors exc. IAT and ICV
-Replaced DME
-Replaced MAF

Main Components:
-M50 (refreshed gaskets)
-Off the shelf TRM tune
-E36 Harness
-VDO Cluster
-'91 318i


I tested my ICV and the resistance values were exactly half of the values in the Bentley. I read somewhere that's a typo in the Bentley though.
I tested my IAT also, and the resistance value was per spec, but that was tested at a fixed temperature.

[lolcantturn]

I have the same problem. I'll psot my setup:


Items replaced:
-Replaced MAF, ICV, O2
-Fuel filter and FPR
-Replaced DME

Main Components:
-M50NV, nothing refreshed
-Off the shelf TRM tune
-E36 Harness
-VDO Cluster
-'91 318is

I'm running O2 12V bypass and I can noticably tell my idle improve after around 10~mins or so, I should time it, which is possibly the heater on the O2.

The ONLY thing I can conclude is harness differences..we're all running E36 harnesses. On my old bronzit car, I used EXACTLY the same wiring diagram, EXACTLY the same O2 in EXACTLY the same location on the exhaust with EXACTLY the same DME. But my harness was E34.

[trackjunkie21]

Ok, well I had a look see at my VSS wiring and it seems I am not getting any power from the cluster at all. Below is a picture of me checking pin 14 at the c101 and x20 connection. Also everyone always states that pin 42 on the harness is VSS input which on my NV e36 harnes is blank., so I decided to trace the black/white wire and came back with pin 73 which would make sense, below is a picture of pin 42 and you can see that it is blank on the harness side. So now I have to pull the cluster and see where there is a break in the wiring.

[lolcantturn]

Ok, well I had a look see at my VSS wiring and it seems I am not getting any power from the cluster at all. Below is a picture of me checking pin 14 at the c101 and x20 connection. Also everyone always states that pin 42 on the harness is VSS input which on my NV e36 harnes is blank., so I decided to trace the black/white wire and came back with pin 73 which would make sense, below is a picture of pin 42 and you can see that it is blank on the harness side. So now I have to pull the cluster and see where there is a break in the wiring.

I told you pin 42 is blank, I AINT CRAZY

Why there would be a break in the cluster is beyond me.
I'm at work and I left my phone in my car so I can't text you but are you getting power at pin 14? Because I am, gotta check pin 73 though

[trackjunkie21]

I told you pin 42 is blank, I AINT CRAZY

Why there would be a break in the cluster is beyond me.
I'm at work and I left my phone in my car so I can't text you but are you getting power at pin 14? Because I am, gotta check pin 73 though

No power at pin 14, on the x20 side and no power on the c101 side which means the wire that goes between c3 on the cluster and the c101 there is a break.

[lolcantturn]

fuck. I have continuity at pin 14..gotta check pin 72 on the ecu

[trackjunkie21]

ok this is weird, it seems on the 5 series harness pin 72 and 42 are switched, atleast that is what the ETM is telling me, although I'm certain that I have a e36 harness.

[lolcantturn]

So if its DIFFERENT, then the E36 harness and E34 harness are NOT the same aside from length. Then the wiring diagrams we followed don't go both ways for E34 and E36...is this a good conclusion to draw then? I mean I've always read that they were identical aside from the length so..

[trackjunkie21]

So if its DIFFERENT, then the E36 harness and E34 harness are NOT the same aside from length. Then the wiring diagrams we followed don't go both ways for E34 and E36...is this a good conclusion to draw then? I mean I've always read that they were identical aside from the length so..

I have both e34 and e36 ETM's open at the moment and it seems that they are indeed switched around.

[lolcantturn]

so is pin 14 on x20 still VSS on both harnesses? No right?

Beej has an E34 harness then I presume since didnt he check Pin 42 on his ecu for continuity and it was good ?