[net.auto] Toyota backfiring

pfoley (11/30/82)

My 78 Toyota Corona has been exhibiting a very strange behavior
that has baffled every mechanic that has looked at it. In very
cold weather, if I shut the engine off before the car is warm,
it backfires. The backfire is out the tailpipe (not into the
ccarburetor) and it is as loud as a gunshot. 
The other strange thing is that this doesn't happen until up to
10 seconds AFTER the car is shut off. It was fixed temporarily
by adjusting (I forgot which way) the spark a little, but after a week
it reverted to its old ways. Any ideas?