Hi:

I think that I'm having an intermittent spark problem with my 1986
Toyota pickup (4x2, 22R).  The engine sounds and feels like it is
running on three cylinders under load.  It doesn't happen all the time
(but very frequently) and only after the truck is warmed up for a
little bit.  I was able to get the engine to stumble when it was
parked in the garage one day by blipping the throttle quickly from
idle.  I hooked up my timing light to one of the spark plug wires and
noticed that the light "stumbled" as the engine stumbled when I
blipped the throttle.  I then hooked the timing light up to the main
ignition wire that runs from the coil to the distributor and noticed
that the light stumbled when the engine stumbled.

The spark plugs have only about a couple of thousand miles on them and
look fine and are gapped correctly.  Although the spark plug wires for
12 years old they have no cracks or other visible damage and test well
within specs.  I performed the factory manual recommended tests for
the coil and the distributor, and everything tested within specs.
Since I didn't find a way to directly test the ingiter, I bit the
bullet and replaced it with a new Toyota igniter (ouch!).
Unfortunately, that didn't solve the problem.

I didn't test the ECU which is located behind a kick panel on the
passenger side.  I'm not even sure what the ECU does anyway on a
carbureted truck.

Since the timing light "stumbled" when I connected it to the ignition
wire coming from the coil to the distributor, does that mean that
there is a problem on the coil/igniter "side" rather than the
distributor/individual spark plug "side" of the ignition?  I could
just replace the coil and see what happens.  Although it's cheap when
compared to the cost of the igniter, it's not THAT cheap.

Any thoughts as to what the problem might be?  Any help would be
greatly appreciated.  Thanks.

-- -- Mike