Quote:
Originally Posted by Michaelflat1
no MAF, only a MAP sensor...
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Oh ok! I get what you're saying now. EGR would affect manifold air pressure, but so would timing.
On my Avalon when warming up it will retard considerably, like 25° after (not before) TDC. The throttle has to open up much wider and increases manifold pressure (less vacuum) quite a bit. This of course uses a lot more fuel, but that's the point. It does it to heat up the catalytic converter and rest of the engine more quickly. The interesting thing is idle engine speeds can be nearly the same in this more-open-throttle, retarded-timing state as it is when the engine is warmed up and the throttle closes and timing advances back to normal.
When I had my 1972 VW Super Beetle I put on a Magnaspark Digital distributor. I was trying to get it to idle lean since most carbs of that era would idle pretty rich for idle speed purposes. But maintaining a stoich or leaner idle was extremely difficult until I figured out that I could program the distributor to advance as RPMs went down which would help maintain a stable idle speed since the engine would slow down slightly, ignition would advance a little, engine speed would go up slightly, ignition would retard a little, and so on.