Intermittent rough idle in neutral after cruise.

MEgearhead

Veteran Member
Joined
Aug 6, 2016
Location
Virginia
TDI
B5.5, 4L, 4G
I have been trying to figure out a rough idle issue for a while now. I recently replaced the turbo and cam. Neither are BHW parts. The turbo is a GT1756 hybrid and the cam is a higher lift/duration BEW.

What happens is after cruising down the road when you disengage the clutch the engine coasts down up to 200 rpm low and runs rough for 15-20 seconds, then recovers.

I have changed the fuel filter and verified there are no leaks. We also ran some diesel purge as the idle stabilization values were spread out considerably. Setting the torsion value at -2.0, 0.0, and +2.0 has no perceivable effect.

After logging several different values the only thing I can find that directly correlates is start of ignition timing. When it is idiling rough the start of ignition is over 3 deg. BTDC. The more advanced the worse it is. After several seconds the timing ramps down to below 2 deg. BTDC and then the engine smooths out and rpm raises up to normal.

What's also interesting is that often EGR and N75 are off while it's running rough then N75 goes to full, and EGR starts regulating once the idle recovers. However, this doesn't always happen, but when it does it always follows the idle recovery. The change in timing always precedes the idle recovery.

I'm interested what others with a manual swap have noticed regarding idle from cruise just after disengaging the clutch.

We set the injector rocker preload with a dial indicator, but I'm tempted to take the cylinder head cover off and verify it along with overall lift of each injector lobe.

Any other thoughts?
 

MEgearhead

Veteran Member
Joined
Aug 6, 2016
Location
Virginia
TDI
B5.5, 4L, 4G
Does anyone else with a manual swap notice a lower idle for several seconds after disengaging the clutch?
 

PickleRick

Veteran Member
Joined
Nov 29, 2017
Location
Greenville sc
TDI
05 GLS BHW sedan 5 speed conversion. BHW Carver SantaCruz in progress
I do not and I use my cruise for about 5 miles of hwy each afternoon. Other than tune, 5 speed and balance shaft delete she's stock.
 

A4QTDI

Well-known member
Joined
Dec 26, 2021
Location
Canada
TDI
A4 TDI
Do charge pressure control test in basic setting. Tell us difference in millibar from on to off.
 

MEgearhead

Veteran Member
Joined
Aug 6, 2016
Location
Virginia
TDI
B5.5, 4L, 4G
Charge pressure test results in 967 and 1107 mbar so 140 mbar difference.

I also determined two other things:

The idle will only smooth out and recover once the car is fully stopped. I was driving on the I95 parking lot this evening and would coast very slowly downhill a long ways in neutral in stop and go traffic, otherwise I may never have noticed that.

After doing the charge pressure test, I was checking out what appeared to be a very slight oil leak at the turbo oil feed pipe, but it didn't appear to be very black. I checked the oil dipstick and at 700 miles after changing it it's as clean as it was right after I changed it. Might be a fueling problem. I know OH mentioned something similar in another thread but I can't seem to find it.
 

MEgearhead

Veteran Member
Joined
Aug 6, 2016
Location
Virginia
TDI
B5.5, 4L, 4G
I took the valve cover off and readjusted the injectors. They seemed to have been adjusted properly and there was no change afterward. It's very bizarre, and I'm at a complete loss.

I wonder if it's a combination of the manual tune and the BEW high lift cam.

I would really like to know if anyone else with a manual tune notices a slightly lower idle rolling to a stop in neutral that comes back up to 861 rpm once the car has come to a complete stop.
 

zzdiesel

Veteran Member
Joined
Dec 10, 2010
Location
sask. mostly now Wa.
TDI
05 passat tdi Geared BSM and Bewcam 2nd 2005 deleted ,converted and bew cam stage 2 Malone3 tune.
My car has the FHN tranny and the BEW cam, though regular, and a 2 tune. I have not noticed any symptoms like you are describing.
 

PickleRick

Veteran Member
Joined
Nov 29, 2017
Location
Greenville sc
TDI
05 GLS BHW sedan 5 speed conversion. BHW Carver SantaCruz in progress
In my paperwork from fast forward I got for putting the BHW in my 4 runner there is a notation on the clutch switch. It says clutch switch 12v at rest and open when pressed. Hint: if you don't want to do this connect to 12v key on else reduced engine power

I think the on was a typo and should be or. Have you checked the function of your clutch switch?


Mine is wired directly to 12v switch power and I notice a good 50 to 75 rpm drop when I pull to a traffic lights. With solid mounts and straight exhaust it's noticeable to me. My cruise control is not working yet so I'm not sure if it will go away when I figure out why my cruise isn't working.
 

MEgearhead

Veteran Member
Joined
Aug 6, 2016
Location
Virginia
TDI
B5.5, 4L, 4G
That's a good suggestion. My clutch switch is disconnected. The switch I installed is closed when the clutch is released and open when it's pressed. For the cruise to work the switch needs to be opposite. I need to either find a different switch or use a relay to invert the signal. I will jumper the switch and see if that makes any difference.
 

CantWrite

Well-known member
Joined
Jun 8, 2021
Location
Placerville CO
TDI
2005 Passat Wagon (BHW/5-spd conv, 03T). I keep in touch with the (2) ALH's I sold.
Not sure this helps......

I purchased the car already swapped. Cam unknown. EEN trans. Cruise Control works as the factory intended (does not rev when pushing in the clutch). The car will start without the clutch pedal being depressed. The factory auto-trans electrical connector has a couple of wires pulled from it, which I assume was required to make something function. (have not investigated it)

My commute includes a mountain pass, and I often will shift to neutral and coast anywhere from 30 - 80 + mph. Whenever I shift to neutral, the car happily idles down normally with no roughness or further drop in RPM.

Side-bar, this thing coasts forever, much better than my ALH's.
 

PickleRick

Veteran Member
Joined
Nov 29, 2017
Location
Greenville sc
TDI
05 GLS BHW sedan 5 speed conversion. BHW Carver SantaCruz in progress
I have noticed after a good 70 mph run sometimes I will have idle down to about 700-650 rpms when coming off freeway. Did it worse when air conditioner was turned on.

She has never stalled and may do it worse/more often than I catch it. As I grow more confident in the vehicle I run with the radio louder and faster highway speeds.

I hope to have cruise control working soon.


Another item that may interfere with the rpm is the tune. The VW ECU needs input for gearing of the transmission that is being used for cruise. The supplier I sent my ECU off to, got all the tune work and custom harness off of along with cruise control and even the little box for universal VSS didn't send me the little box that makes my Toyota transmission read gear ratios that the ECU recognizes.

Currently when I engage and try to set the cruise she sets off a soft cel that the cruise input isn't recognized or something of the sort, there are 2 cels and both related to crusie but do not set off the cel light.


I didn't really understand why this couldn't have been programmed into the tune but never the less this could be my issue. We'll find out.

I'm running at a much lower rpm on my 4 runner than I am my dvz Passat but if the crusie repair doesn't work I'll maybe swap the ECU to see if it's a software issue.
 

PickleRick

Veteran Member
Joined
Nov 29, 2017
Location
Greenville sc
TDI
05 GLS BHW sedan 5 speed conversion. BHW Carver SantaCruz in progress
Swapping tandem pump made no change. Replaced due to oil leak. Slow but annoying
 

PickleRick

Veteran Member
Joined
Nov 29, 2017
Location
Greenville sc
TDI
05 GLS BHW sedan 5 speed conversion. BHW Carver SantaCruz in progress
After an odd power loss when hitting hard bumps I found a bad connection on the cps sensor plug.

Replaced cps with a spare and do far the rpm drop at idle has not reoccurred. Will keep you updated next week.
 

MEgearhead

Veteran Member
Joined
Aug 6, 2016
Location
Virginia
TDI
B5.5, 4L, 4G
I finally was able to invert the clutch switch signal to the ecu. It still idles about 200 rpm low until the car comes to a complete stop then it recovers. It must be simply a function of the manual tune. I recently replaced the crankshaft position sensor so that should not be an issue. The cruise is now working correctly.
 

PickleRick

Veteran Member
Joined
Nov 29, 2017
Location
Greenville sc
TDI
05 GLS BHW sedan 5 speed conversion. BHW Carver SantaCruz in progress
Do you have vcds? Not sure if it's the cold weather we're having now but since I installed a clutch switch and verified the values in I think group 2 of 006 my rough idle immediately upon coming to a stop has been gone.


My crusie control still doesn't work, I'm thinking it's a tune program issue, but that rpm drop has not come back.


It would do in city traffic as well as getting off the freeway
 

MEgearhead

Veteran Member
Joined
Aug 6, 2016
Location
Virginia
TDI
B5.5, 4L, 4G
I do have VCDS. That's how I was able to figure out what was going on. The clutch switch is working correctly. The cruise works and cancels if the clutch is pressed. Still idles about 200 rpm low and a little rough. Not nearly as bad as it was without the clutch switch working properly. It was over 400 rpm low and pretty rough. I had the idle increased to 1000 rpm with the tune. I think what I'm left with is just the nature of how these manual tunes are done. If it would have been like it is now, and I had left the idle stock, I might not even notice it. It has been much cooler since I got the clutch switch set up right, so I'll have to see what it does next summer.
 
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PickleRick

Veteran Member
Joined
Nov 29, 2017
Location
Greenville sc
TDI
05 GLS BHW sedan 5 speed conversion. BHW Carver SantaCruz in progress
I'm hoping in my case it's not a cold weather thing. It made me nervous pulling up to a stop sign or traffic light to have the rpms stumble. Usually it was 100 or so rpms but occasionally 200 to 250ish.

I just swapped my differentials from 4.10 to 4.30 a few weeks ago and then swapped transmissions this past weekend so I've been playing closer attention to my tach than usual.

It's odd that it never did that in my 5 speed converted Passat.
 
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