Cold engine - output drops so low for a brief period. Ideas?

[IdahoDoug]

In the last month or so, the van has been exhibiting a strange symptom. It's had a recent tune, fuel pump, filters and such and the oxygen sensor has been disconnected for over a year. It was also rebuilt a few thousand miles ago, so grounds have been cleaned, injectors cleaned, etc. It's been running like a top.

Here's what happens. Only when cold. I'll start the van and pull out of my driveway. About 15 seconds later, I arrive at a stop sign and the engine is very low RPM as if it wants to stall (automatic). Pressing the gas gives a slight change to the engine note but hardly any power. Flooring it doesn't change anything either. It will barely roll out away from the stop sign at about the same pace as if a couple buddies were pushing it away from the stop sign. Almost feels like it's flooded. Instantly putting it in neutral, it will barely rev with a lot of throttle when it should rev instantly. When it gets up to a couple thou RPMs it seems to clear its throat and I can rev it up and down as normal. Put it back in gear and it pulls strongly as normal.

Any thoughts? I'll be putting a new prefilter on it to replace the one that's been on it for the 3000 or so miles since the rebuild. More out of curiousity because I can see some sediment in it.

Thanks.
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1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1993 Toyota LandCruiser, 2002 BMW 325iX, 1982 Toyota Sunrader

[DanHoug]

my first guess is a mixture issue.. i'd really hook a good O2 sensor back up. but, barring that, you might want to play around with your AFM spring tension. mark where the clip is now with a dot of paint/white out then move the black disc one or two clicks counter clockwise. this will richen things up. drive it and if worse go 1 or 2 clockwise from base position.

i've found that during open loop running, when the engine is first started, that this adjustment is critical to acceleration off idle. once the O2 sensor heats up, it doesn't seem to make too much difference.
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-dan
60% of what you find on the internet is wrong, including this post.

'87 Westy & '89 Westy both 2.1 4spd

Past projects can be found at--
www.thefixitworkshop.com

[Abscate]

Possibility. If excess cold start fuel washes oil off the cylinder walls, you lose compression and will idle with no power. I don’t think it happens to boxer engines but it’s well documented in BMW and Audi.

Google lawn mower or holiday syndrome for more.
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[Wildthings]

I wouldn't think it would be O2 sensor related as the TSII sensor is likely not reporting that the engine is hot enough for the system to go closed loop.

[danfromsyr]

TS-II could be faulty and reporting a warm engine too soon.

measure values at cold.. then at the end of the block when it stalls.

I've been meaning to make a TS-II jumper pig tail for on the fly meter readings.
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[IdahoDoug]

FYI - O2 sensor has been disconnected for over a year and it's been running like a champ. Not sure if all of you saw that. Carry on.
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1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1993 Toyota LandCruiser, 2002 BMW 325iX, 1982 Toyota Sunrader

[DanHoug]

since it was running great then changed rather quickly, i'm giong to withdraw my AFM suggestion... the spring tension doesn't change radically like that, tho it is always useful to tune it. the wiper arm might need a cleaning however.

i'm going with the TSII also, that just makes sense but also consider running some Techron thru your system in case the injectors are getting dodgy.
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-dan
60% of what you find on the internet is wrong, including this post.

'87 Westy & '89 Westy both 2.1 4spd

Past projects can be found at--
www.thefixitworkshop.com

[AZ Landshaper]

x2 vote for the fuel mixture.

any black smoke as you accelerate from the stop?
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[dougass]

I have very similar issues when cold. I have not done much exploration regarding wiring, however, I have replaced most of the components related to air-fuel mixture. Runs fine after a minute or so...

Was considering sending injectors out for a cleaning until I saw Marco's :high performance injectors". Will let you know if this resolves it.
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'91 GL - 2.1 automatic named Klaus for weekend adventures.

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[jlrftype7]

[danfromsyr]

quick question re: the resistor, do you add it to the GND side or the ECU side of the sensor?
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[jberger]

Why is your o2 sensor disconnected? I would suggest that the overly rich running that happens with the sensor unplugged is masking other issues. At your elevation I can't imagine it would run well at all without the Lambda feedback... all things being in good working order.

J

[IdahoDoug]

Last summer we were up in Canada and the van was struggling climbing hills. Someone here recommended I just disconnect it and run rich. I don't have any test equipment other than a multitester, it worked great (immediate change) and I've just left it that way even though I'm getting 15mpg.

On the tailpipe cloud - I'll watch for it today. Also, my fuel injectors were professionally cleaned a few thousand miles ago.

Doug
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1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1993 Toyota LandCruiser, 2002 BMW 325iX, 1982 Toyota Sunrader

[Abscate]

[Wildthings]

With the pedal to the floor the O2 sensor should not have any effect on how it runs, but it would at part throttle. I am thinking that you may have an out of spec TSII sensor and a bad TPS. Both would throw the mixture off when at full throttle climbing a hill and would throw the mixture off when you decelerate when cold while approaching a stop light or sign.

Disconnecting the O2 sensor would also mask a misfire. Since the misfire would likely be worse on a cold engine than a hot one this could also be your problem.

[jlrftype7]