Mazda Protege 5 random misfire not so random

I am having a problem tracking down a misfire code on my wife’s Protege 5. It keeps giving me a P0300 random misfire. I replaced the coilpacks, the plugs and the wires, but it still throws the code.

Now its decided it wants to idle rough and instead of the cel being solidly on, its flashing.

Anyone else having this problem?

If the CEL has been flashing don’t drive the car until you get it sorted out. You can do a great deal of damage.

Its sort of to your advantage that it has started idling rough since the random misfires are terrible to track down.

It seems that you probably took care of spark, though you’d also want to check the wiring to your coil packs to make sure that the voltage is steady and correct.

You’d also want to check the fuel pressure and the operation of the fuel injectors. The simplest way to do a quick check that the injectors are running (at least electrically) is to use a little piece of hose as a stethoscope - with the car idling stick one end on the injector & the other in your ear. Each one should give you a steady tick tick tick.

Have you been losing any coolant? Any sign of coolant in the oil or vice versa? (The oil would look something like a chocolate shake). I’d want to put a vacuum gauge on it (cheap and easy to use) - with that you can get a very quick read on the possibility of a head gasket or intake gasket problem.

The get a real read on mechanical problems check the compression, though a vacuum gauge gives a quick - though general and impreceise - read of that too.

What engine does that have in it? What year? Mileage?

Have you read the codes again since the rough idle started?