A Trick for Idle control

[Jim]

A Trick for Idle control :
This is probably not needed for manual trans. cars ,
but maybe useful anyway .

I like to run my Timing way advanced at Idle Speeds because it makes the
Exhaust Note very quiet instead of a "heavy droning sound" drowning out
my Stereo , it also keeps the engine cooler and uses less gas while
sitting at traffic lights or in a traffic jam during rush hour .

Unfortunately , it also makes the idle speed less stable , that is ,
if the Throttle Body is adjusted for an 800 rpm idle speed in gear ,
(auto trans) , in neutral or park the engine will idle at 13 to 1400 rpm .
( Of coarse when I install my high stall speed converter this won't be
as much of an issue . )

With a "Stock Converter" idle speed stability is unacceptable .

Here's an 80 to 90 percent fix , super-easy and cheap :
Go to your local auto parts store and buy 2 or 3 additional PCV Valves and
some Tees and vacuum hose , the rest is up to you .

Most PCV Valves are designed to be "constant volume" flow regulators ,
the higher the vacuum goes the more they restrict flow , and vice-versa .
Inspect the valves you get carefully because some are just a restricted
hole which is worthless and actually makes the situation worse ,
make sure it has a spring and a moving valve that rattles around inside .
If your engine uses the "Plain ol' Restrictor Hole" type of PCV valve
you would be better off getting rid of it and replacing it with the
"constant volume" flow regulator type .
I use 3 , old school , generic , GM V-8/V-6 PCV valves with a plastic
90 degree , 3/8 inch hose barb on top on my 4.3L V-6 ,
but they make the same valve with a
3/8" hose barb on both ends (check flow direction) .

Adding just one of these may be adequate for a small 4 banger ,
Big Block V-8's may need 4 or 5 of these valves added on .
The object is to provide 90 to 95 percent of the engines Idle Air ( HOT )
through these PCV valves and have the Throttle Body butterflies just barely
cracked open so that they won't try to stick shut , and ,
you still have "some" degree of idle speed adjust-ability .

It's not electronic feedback loop control but
it works excellent on my engine with some leaning down of the mixture
at high vacuum/high idle RPM in the VE Table thrown in for a
little more control .

In Gear :___825 to 850 rpm , 13.5 to 1 AFR / 35 degrees advance
Out of Gear :900 to 950 rpm , 16.5 to 1 AFR / 35 degrees advance
Moderate/random Idle Surging when warming up , mostly due to my
spiking map sensor ..........but that's another story .

( I run my engine VERY lean , your results may vary )

Watch out for Knock when you stab the throttle ,
->if you have.....
smaller displacement/high compression/short stock cams ,
it WILL RATTLE with this much advance , listen carefully .

[wagon]

That is a lot of advance!!! The later firmware versions and Megatune allow you to set the idle control pwm settings for coolant temperature. I found this helped me no end in achieving a decent idle (otherwise, I ran high idle in neutral and just about busted the auto trans putting it into gear). Then you won't have to run so much advance.

Kendall.

[rs2000]

Yeah that much advance will kill you economy at idle too, not help it.

[Jim]

To : RS2000

If the engine runs faster and faster the more you advance the
timing and you have to close the throttle more to slow it down ,
how does it "kill the economy" ?

Yes , under load there is a point of diminishing returns when you
keep adding more advance .
Most engines will knock and rattle to let you know you've
gone too far.
Advancing the timing right up to the point of knock usually
produces the best power and economy , this is exactly how
car manufacturers setup their knock sensors .
At light throttle cruise , usually there is not enough load on
the engine to make it knock , even with way too much advance ,
so you have to rely on experience and "feel" .

By the way , I average 23 mpg in a 2ton brick .
(3900lbs. with driver)(station wagon)
This includes alot of highway driving averaging 80 mph ,
(yes it's standard routine around Atlanta)

[rs2000]

Thats just what i was told elsewhere. I was finding out about vacuum advance and was told to run the vacuum advance off a ported vacuum source as vacuum advance at idle was detremental to fuel economy (and idle stability but thats a different kettle of fish).

When you say it how you did it does make sense that increaced idle advance would be more economical..

I also found when i was playing with my car that will less advance (6 DBTDC) i could run a much leaner idle, as to keep the engine idling stably with more advance (20 or so DBTDC) (not hunting/stalling) required it to be much richer. but then i guess that could just be my engine (which is old).