Check engine light flashing when engin stumbles

I noticed some stumbling of the engine when maintaining speed up hill
or accelerating in a high gear. One day the check engine light started
flashing and then stayed on. The day I was to take it into the shop to
get the codes checked checked, the light went off and stayed off for
about a week but the engine still stumbled under the sames conditions.
About two weeks later the light came back on and I got it into the shop
to check the codes and it came back as an engine misfire. They
sugested I change the plugs. As I had just changed the plugs 6000
miles earlier I thought this was a bit strange, but the service manager
told me that if I had used Bosch platinum plugs that was most likely
the root of the problem. So I changed the plugs again using the NGK
plugs recommended in the owner's manual.

The engine purred likem a kitten

For about a hundred miles and it started all over again. I'm now
thinking that it could be either the Crank Position Sensor, Throttle
Position Sensor the Coil Pack. God help me if it's the control module.

Gas mileage is still fine and the problem with the stumbling is
intermittent but chronic. It has yet to stall during one of these
episodes.


Am I on the right track with suspecting of the sensors the sensors?
Also I am aware that the timing belt is overdue for service. Can those
things stretch to a degree that this kind of thing might happen? I
remember having an old Dodge Colt with a stripped crank pulley and the
engine would stumble in much the same manner.

 

What year, model, engine?
Did you change the plug wires when you changed plugs? You didn't say what
the DTC was but if its P0300-P0306, I would suspect the wires first, then
the coil.

 

Misfire codes, especially those that can be felt as a lack of power and
engine vibration, tend to be caused by the secondary ignition components
(plugs, wires, coils).

Since the problem went away briefly and then came back, I'd suspect that
you may have a carbon-tracked spark plug. When this occurs, a line of
carbon runs down the inside of the wire boot along the spark plug from the
tip to the hex, providing an alternative path for the electicity. In your
case, there may have been such a line in the wire boot so that it only
took a short period of time to recreate the path when the plugs were
replaced. In that case, you'll probably need to replace the plugs and
wires.

 

You may need to replace the plugs and wires at the same time. What you
describe sounds like the classic symptoms of a carbon-tracked spark plug
and wire. When this occurs, a track of carbon runs down the porcelain of
the plug from the external tip to the hex, providing an alternative path
for the electricity. The carbon will be on the plug and the wire. If
just the plugs are replaced, the track on the wire remains and will become
active again in a short period of time. If just the wires are replaced,
the track on the plug remains and will become active again in a short
period of time.