I have been dealing with a Check Engine Light and misfiring codes for a few weeks now, started with a simple P0303, cylinder 3 misfire. Replaced ignition coil, no real change in performance until I reset the battery then CEL went away for about a day. Ran better but still lacking with a real rough idle upon start up, not leaking heavy amounts of coolant anymore at least.
Ran alright for a day or two then the CEL returned and running extra rough and shaky.
I then replaced all ignition coils just in case. Still running awful, I reset the battery again, CEL goes away for about a day with seemingly slightly better performance, less coolant leak then when CEL is on, I think.
Cannot figure out what is causing these misfires.


My latest computer error read "P0300; indicating too many random misfires within a predetermined period of time."
Misfiring in cylinders 3&4 /catalytic converter damage.
At the top of the Auto Zone print out report it reads "Replace Engine Control System".
Looking up the ECM, it's easily $1,000+ for the part, plus labor.
I am almost certain it is something I just haven't come across yet.

Should I try new spark plugs? That is what I went in to Auto Zone to try next but after seeing the "replace ECM" message I decided to go home and research more.
Anything else that could cause this random misfiring?

Please please please, any advice to save me from the financial smite of the mechanical gods!!

 

Don't trust AutoZone. If there is a misifre, you need to find out why. Spark plugs would have been the first place to start. I would recommend OEM. I would also recommend a dealer for diagnosis, especially since it is free up to an hour.

If plugs don't fix it and the coils are firing, then you need a compression and cylinder leakage test and the repair will likely be more than if it was the ECM.

 

Solved- Replaced spark plugs and one faulty ignition coil.
Thanks for the support!!