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Correlation between proper timing and surging

    I decided to tinker with my timing today to check something out.  I have
always had a surging problem when decelerating, engine runs down to 1500rpm
and then it surges once or twice and then drops to idle.  I noticed that
when I was using the 16V ECU there was no surging at all and this was
because the 16V ECU had very a different timing map.  Also it was impossible
to run stock timing, 6BTDC, with the 16V ECU so I ran it around 4BTDC.
    Now what I decided to do was advance the timing to see what it did to
the surging.  The further I advanced the timing the smaller and less
apparent the surge became, although the further advanced the timing went the
less power the engine put out.  Also with the timing at stock the idle runs
too high, but not by much.  Also with timing at stock when I come to a stop
very quickly there is a little idle drop and bounce.  What is going on here?
    Another part of this equation is that when my ISV is disconnected the
engine behaves very strangely at idle.  The idle bounces wildly up and down,
when timing is at the stock position.  After I advanced the timing a fair
amount the idle became smooth with the ISV disconnected.  The engine acted
as it should with the ISV disconnected, runs a high idle, but runs smoothly.
Now this seems to tie into everything some how.  So if timing is at stock
and there are all these little idle/deceleration quirks, does this indicate
some of the fuel system components need to be adjusted to compliment proper
timing?  Anyone who can tie this equation up for me?


Alexander van Gerbig -- '88 Audi 80

The Audi 80 Pages-----------------------

Katonah, NY 10536