Hunting for idle when coasting, VSS related?

[trackjunkie21]

Well Beej's thread got me thinking that something isn't wired up/working right in my swap. Time and time again I have been checking for vacuum leaks, faulty sensors and the works only to be struck down and basically put back to square one. Lolcantturn asked me to check if my VSS is functioning properly, procedure was to speed the car up to say 25-35mph and coast in neutral to see if the idle rises to ~1,000rpm, once car comes to a standstill, idle should drop back down to normal. I proceeded to do this test and when the car was cold not much happened, idle never "rose" to the desired 1,000rpm but stayed at a regular idle which to me seems a bit low, once the car warmed up, the car would surge and hunt for idle until I would come to a standstill and finally idle would return to normal, Here is a video of what I am talking about, I let the car coast from about 35mph to a standstill and see for yourself what is going on.

Input?

[Adrian_Visser]

Fuck I have the same problem, except my VSS is definitely working.

I have the idle bump to 1000 at a slow roll but when I touch the brakes and let off at that speed I get wicked idle bounce. I reset my DME the other day and first drive had it really bad like you have in your video just coasting to a stand still without the brakes To me this indicates a vac leak that at the time the DME hadn't yet compensated for.

At a stand still my idle is rock solid. I also get a mean rev dip if I drop the car into neutral idle from higher revs when coming to a stop. I have had the engine die several times when on warmup doing this. I am running an 11lb flywheel however and have a chip tuned for it with 900rpm idle.

I haven't gotten around to even trying to diagnose it though, my thoughts are the usual:
Vac leaks (The turkey neck for the icv into the intake is the most likely candidate in my case)
or a sticky/slow icv or possibly a leaky booster.

Good luck I look forward to seeing what you find.

[328ijunkie]

hows your VSS/C101 wired?

[trackjunkie21]

hows your VSS/C101 wired?

Nando wired it up for me, I'm guessing it's good but I shall check that later. I'm going to connect my scanner to see if I get a speed reading.

[Beej '86 325es]

Nando wired it up for me, I'm guessing it's good but I shall check that later. I'm going to connect my scanner to see if I get a speed reading.

I don't know if I'd trust the scanner.
My mechanic ran it on his scanner and I ran the Peake scanner, neither of them said anything about the VSS that wasn't even hooked up.

Mine does that a little when it's cold...possibly linked to my issue of the ECU not reading the O2 when cold.

[trackjunkie21]

I don't know if I'd trust the scanner.
My mechanic ran it on his scanner and I ran the Peake scanner, neither of them said anything about the VSS that wasn't even hooked up.

Mine does that a little when it's cold...possibly linked to my issue of the ECU not reading the O2 when cold.

Well the scanner connects to the ECU, all I want to know is if the ECU is actually getting a speed signal, after 15mph the scanner would say cannot read for whatever reason because certain speed exceeded, if the VSS isn't working, how would it know?

[trackjunkie21]

Ok hooked up my Snap-on and went for a drive, speed is being displayed on the scanner which would mean that the VSS is functioning I'm sure. But idle doesn't rise when coasting. I looked at the c101 and it looks as though pin 14 on the body side is black/white(VSS) and in the adapter is also VSS. Forgot to check the engine side to see if the wire is actually there.

[jrdeamicis]

This is documented somewhere as a goofyness of OBD1. I will try and find it.

[trackjunkie21]

This is documented somewhere as a goofyness of OBD1. I will try and find it.

please and thank you!

[xwill112x]

All my cars do this, My 4.0 cherokee, my old m42 car, as well as my dads OBDII 328i

[trackjunkie21]

All my cars do this, My 4.0 cherokee, my old m42 car, as well as my dads OBDII 328i

Doesn't mean they should.

[lolcantturn]

This is documented somewhere as a goofyness of OBD1. I will try and find it.

please do

[Beej '86 325es]

This is documented somewhere as a goofyness of OBD1. I will try and find it.

Please.

I think that makes 4 of us here with identical issues.
I'm curious if your O2 heater relays click on after 9 minutes like mine.

[trackjunkie21]

Please.

I think that makes 4 of us here with identical issues.
I'm curious if your O2 heater relays click on after 9 minutes like mine.

Thanks for reminding me. I had connected my snap-on and started the car what do you know? 02 sensor not ready, meaning heater has not engaged. It had engaged after a few minutes much like yours.

[Beej '86 325es]

Thanks for reminding me. I had connected my snap-on and started the car what do you know? 02 sensor not ready, meaning heater has not engaged. It had engaged after a few minutes much like yours.

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
EDIT: - Checked IAT sensor

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

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.