[T3] rough idle at cold start up

[Dennis Stiefel]

-----Original Message-----
From: type3-vwtype3.org-bounces at lists.vwtype3.org
[mailto:type3-vwtype3.org-bounces at lists.vwtype3.org] On Behalf Of Jim Adney
Sent: Monday, February 10, 2014 9:50 PM
To: type3 at vwtype3.org
Subject: Re: [T3] rough idle at cold start up

On 9 Feb 2014 at 22:06, Dennis Stiefel wrote:

> The only thing about the running part has been going on since we got 
> it going. When you first crank it up cold it pufs out black to dark 
> gray smoke Idles rough then after about a minute it smooth's out and 
> all is well. It was worse when we first put it on the road but got a 
> little better after the engine reached over 100 miles. Then last week 
> I done a
> 500 mile oil change and valve adjustment after that the cold rough got 
> back worse like it was when with the first 100 miles.

The smoke is due to oil getting into the combustion chambers and burning
when the engine is first started. A certain amount of this is normal, and a
little more common on freshly rebuilt engines, where the rings have not
fully seated. It can be worse if the car tends to be parted on a slope to
one side, but mine sometimes do this for no particular cause.

I would check a couple of things:

1) Make sure you have not been overfilling the air cleaner. It should be
filled up to the "step" and no farther. If you put in more, you're likely to
suck some into the intake. Also, NEVER turn the upper half of the air
cleaner upside down while you're servicing the air cleaner. Turning it
upside down, allows oil to drain into the intake passage where it will get
sucked into the  engine when you next start it.

2) Make sure you're not overfilling the crankcase. The dipstick is spring
loaded so that it always measures off the bottom of the dipstick tube. I've
seen dipsticks which had gotten bent, so that they were stuck "retracted
upwards." That would put an extra half quart or more oil in the crankcase.

3) If you left out, or mis-installed, the louvered plate under the breather
stand, this will cause excess oil to be thrown up into the breather box.
This oil could then be sucked into the intake, especially on '72-3 engines
with the PCV system.

> I've tested the aar by when it is cold and just been cranked I take 
> pliers and squeeze one of the hoses going from it ti the intake and 
> the engine just bogs down. Then I do it with it warmed up at operating 
> temperature and no change. I guess the aar is working but I wonder if 
> it is partly stopped up not letting enough air (but some) in. Has 
> anybody seen this? After the first minute or so it's all good. Maybe 
> I'll take a video and post it sometime this week to show what its
> doing.   

Forget the pliers trick: That will just ruin the hose. Instead, pull off the
hose that goes to the air cleaner (at the air cleaner end) and cover it with
your thumb. That is more effective and non-destructive.

When the engine is cold shutting off that air should make the idle speed
drop. When the engine is hot, this should have no effect. 
That's all you need to do to check the AAR. Efforts to be more subtle than
this are just a waste of time, as the AAR has absolutely NO effect on the
engine's performance except at idle.

The AAR has NOTHING to do with richness. It is simply a device to give you a
little more power when the engine is cold in an attempt to hold the idle
speed somewhat constant. It's not sophisticated, so the cold idle speed
always tends to be slightly elevated, which is not a problem unless the warm
idle speed has already been adjusted too high. The air that comes into the
IAD via the AAR is indistinguishable from that which comes in via the
throttle butterfly or the idle air passage. The pressure sensor adjusts the
fuel delivery for whatever air gets in, and doesn't care how that air gets
there.  

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

_______________________________________________
Whoa lot of info for my little ADHD brain to proses LOL.  OK first just
checked the oil level on the crank case and air filter when I done the oil
change and valve adjustment.  Since I recently done the overhaul I remember
installing the louvered plate you are talking about in the way the Bentley
described.  I think probably if it was any of these things it would be the
rings not seated good yet. As far as the pliers go I doubt I was that rough
with the hose to damage it if I did the hose probably wasn't any good
anyway. Been doing that to vacuum hoses on various cars and trucks for
nearly 30 years and haven't lost a hose yet.  However I can try it your way
but I think I already have established that there is air going through it I
just wonder if it's enough when the engine is dead cold when it first
starts. It idles fine after it runs for a minute or so.  The issue with the
pressure sensor ( and I'm NOT an expert on the D system or any other but I
have worked on several different types of FI systems) since it reads vacuum
in the intake wont the vacuum be low when the idle is rough?  And if the
vacuum is low and or erratic will the ECU want to enrich the fuel mixture?
Not trying to be a smarty pants just trying to think this through. Maybe I'm
over thinking this. It's really not a big deal any way since it just dose it
for the first minute or so it runs.  

Dennis Stiefel
72 Fastback FI MT
71 STD. Beetle
67 Ford F-100 (hart of Crown Vic)
Rainsville, AL