My wife's Protege has been intermittently throwing the P0300 code - maybe once every two weeks for the past two months. 86k miles currently.

Typical symptoms as others report from what I've been reading: Cruising along the highway, sudden loss of power and flashing CEL. Giving extra gas brings rpm back up and stops the stumbling. It even happened to me once while I was driving it. Pull over, shut off, restart engine, CEL is solid, but runs fine. Read and cleared codes with my Droid X/Torque/BT OBD2 adapter.

I have changed the plugs (accidentally went 10k on NGK BKR5E when I usually change every 7.5k). That didn't fix it. Did some testing on the ignition coils tonight with the shop manual. The short wire (to cylinder #3) resistance was too high (7k ohms, supposed to be 1.9-4k ohms). The two coils and other wire checked out ok. Could it be that easy? Wouldn't the code show up as a P0303 in that case?

We have also noticed a definite sulfur smell on occasion upon pulling into the garage and shutting off the engine. Doesn't seem to have any direct correlation with the codes though. Separate issue or another symptom of same? Thoughts? Thanks.

 

A flashing CEL means that the catalytic converter is in danger.
Now if one cylinder is not firing at all you have a lot of fuel entering the converter and there it is being burned. The resulting heat could melt the converters honey combs.

I am sure you changed that wire already. Is the engine running better now? And is the smell gone?

 

I've been having the same issue, plan on changing the coils see if that clears the problem. Seems to have worked for TristanP, since he didn't come back to comment. Resistance was only slightly high then spec, but I've yet to get out my Megger out to test the the coil insulation.

 

Thanks ADC, I would be interested to know if it worked.

 

Sorry, for the lack of an update. The day after I tested the packs and wires, my wife took the car to be inspected and reregistered. I had driven it enough the previous night so all the readiness codes were set. It passed fine and hasn't repeated the issue since. *knocks on wood* I still plan on buying new wires and coils this week.

 

New coils and wires installed this morning. Running fine so far. Also replaced the air intake hose leading from the airbox to the intake manifold that I mangled last week when I changed the air filter. Had temporarily fixed it with duct tape and a layer of metallic HVAC tape. The engine had been dying at idle in Drive and stumbling at idle in Park. The heat and age had made the hose brittle enough that there where three significant cracks in it. Got the parts from RockAuto.

 

I have an '03 Protege that was doing the same thing, random stalling out at speed (p0300) then fine for long periods. Replaced everything I could think of. It turned out to be the rear defroster.

 

So far so good. New coils seems to have done it.

 

That seems pretty random. I didn't know a short could lead to such a problem.