why does advancing timing cause funny idling?

[GTS Jeff]

right now, my car is about 8 degrees advanced over factory specs of (10 btdc).

what ive noticed is that the idle gets a little bumpy (u can see it bouncing up and down about 50rpm on the tach, but u cant feel it in the car) which i can understand. but whats WEIRD is that the idle is higher while the car is coasting (around 1200rpm), then drops when the car stops (900rpm), then slowly climbs back up again (1100rpm)

it only does this when the timing is advanced a bunch, on my car, an ae86...and the same thing happened on my friends vw gti when the timing was advanced on that car.

what causes this? keep in mind that my timing isnt advanced too much, like im not pinging or feeling any misfires..

[legendboy]

Well one reason is that advancing sparc at idle will lean the a/f out alot. Most cars like a nice rich 11 afr idle.

[Moe Man]

thats maybe why you should keep your car at factory specs..........:thumbsup:

[googe]

Originally posted by Moe Man
thats maybe why you should keep your car at factory specs..........:thumbsup:

i think youve lost your right to speak :(

[rice_eater]

advanced timing using a cam gear or advanced ignition timing?? two different things :dunno:

[GTS Jeff]

Originally posted by rice_eater
advanced timing using a cam gear or advanced ignition timing?? two different things :dunno: advanced ignition timing.

so the misfiring makes sense...but what about the higher idle while coasting vs being stopped?

[Primer_Drift]

Is there a vacuum advance affecting that at all? I'm not too familiar with how the 4age's control idle. Any more info there? 8 degrees timing at idle will definetly lean it out enough to cause idle fluctuations. Possible that timing change from cruise loads to idle loads causes a big enough change in afrs to affect idle rpm once the idle control (whatever it is on toyota) kicks in, thus the fluctuation from 1200-900-1100 rpm.