Strange timing issue ?

[jondee86]

Some known facts... the ECU has pre-programmed fuel and ignition maps
that control the injector duration and ignition timing according to a
combination of rpm and MAP. The TPS tells the ECU how far open the
throttle is, and how fast the throttle position is changing.

Some speculation... the ECU will also have some preprogrammed "trim
tables" that add or subtract fuel/timing under certain circumstances. One
of those circumstances will be idling. To ensure a stable idle and on and
off throttle transitions, the ECU will switch from a RUN map to an IDLE
map. The idle map will probably have reduced advance and increased fuel.

The ECU knows to switch to the IDLE map when the IDL switch in the TPS
is open (= closed throttle), and the engine rpm's are below some set
figure. So, one explanation for the odd behavior of your ignition, would be
that the throttle was closed, but the ECU was still on the RUN map i.e. it
was not receiving a closed throttle signal from the IDL switch in the TPS.

The only flaw in this theory is that the ECU should not go into diagnostic
mode if the IDL switch is closed (= throttle slightly open). Maybe you
have some wiring defect in your TPS circuits ? Anyways, the above is
the best I can do on short notice

Cheers... jondee86