[T3] Engine Idle very low, once warmed up

Jim Adney jadney at vwtype3.org
Sat Aug 5 09:30:38 PDT 2017


On 4 Aug 2017 at 13:11, jaredkohler at gmail.com wrote:

> My auto trans AAR was not working as we all suspected. I began the
> diagnosis after starting the engine (cold in AM) and allowing to idle for a
> few minutes. I then pulled the hose from the AAR to the oil bath and
> plugged it with my finger. Engine immediately died. This scenario continued
> the longer the engine idled and the more warmed up the engine seemed to
> get.

> I then checked my AAR power source which I had made during my FI
> installation. It had juice.

Here's what I think was happening:

You would drive until everything would warm up. With a hot engine 
compartment, the gooey stuff in your AAR would soften and eventually let 
the AAR close. That would give you the very low idle speed.

When you parked the car, with the electric power removed the AAR cooled 
faster than the engine and opened. Once everything cooled the AAR was 
once again "glued" open.

When you tried to duplicate this during a tuneup, with the engine lid open 
the AAR never got hot enough to free up the glue.

So my guess is that your AAR was working, but it was sticky and this led to 
its having a very slow response time.

One thing to understand, that Ray Greenwood was trying to explain on the 
Samba, is that the AAR is not necessarily supposed to increase the idle 
speed; it's supposed to hold the idle speed somewhat constant, in spite of 
the increased viscous friction of cold oil in a cold engine. It's an imperfect 
system, however, so the cold idle is almost always higher than the warm idle. 
(Which is better than the alternative.)

> Now, I turned to my parts bin and the mechanical (Manual car) AAR I had. I
> figure, my Fastback is a manual car, why the heck do I have an Auto AAR?
> This should have been my thinking during my FI installation. Strike 3! But,
> we all learn from our mistakes. So, I began the process of removing the
> Auto AAR and installing the Manual AAR.
> 
> Now with the Manual AAR installed, the engine would continue to idle with
> the oil bath hose plugged with my finger, although very low. While the
> engine was nice and warm, I adjusted the idle set screw (with lock nut) a
> half turn. Wow! Now, I had an idle my ear and memory were happy with.

I always close the AAR hose with my thumb while setting the idle, even with 
a warm engine, simply because I want to check that the AAR is working and 
also to get it right, in case the AAR closes a bit more after I turn my back on 
it.

> Still, I know I should get a Tach or an automotive multimeter to truly dial
> it in. On my list and will purchase. I'll revisit the engine's true idle
> rpm once bought.

Dwell/ Tachs are uncommon today, since modern cars no longer need them, 
but ebay is a good source for them. Search ebay for 

Penske Dwell Tach 244-21013

If you also need a good timing light, there's a great bargain on a Penske 
inductive timing light along with that dwell meter. They are both good tools.

> Long story a little shorter and several test drives later, my Fastback no
> longer has low idle as I idle at stop signs and stop lights! Wow, what a
> difference! Yet, once I shut off the engine, shop at Home Depot, return,
> start the engine, I get a 30 second (yes, I timed it) rough idle until the
> AAR begins to warm and begin it's function. Once the AAR comes alive, the
> idle speeds up, smooths out, and away I go without any dip in performance
> throughout my travels home.

A sticky AAR could give you a low or high idle, but not rough running. I doubt 
if this had anything to do with the AAR. It's much more likely that you had a 
few fuel vapor bubbles in the lines that had to be purged before you could 
start running on all 4 cylinders again.

You should be following William J's thread on the fuel vapor topic.

-- 
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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