2.0L Help! p300 code, rough running, CEL flashing...Clear code, back to normal?

Hey guys,
Can I anyone shed some light on a weird situation?

Canadian 2001 2.0l LX w. 180km: recently idles seems low, suddenly car seems to switch to low power (ecu adding fuel= lean condition?) and multi-cylinder misfires and starts whistling (sucking air through a straw) under load. Check codes(p300 only), clear code, runs well again, no misfire and plenty of power and whistling stops... for awhile, then it just happens all over again. Changed all 3 VTCS actuators, don't think its plugs, wires or coils because of you clear the code, it goes away. Could unmetered air be entering through some actuated valve somewhere controlled by ecu? Tried cleaning egr, not sure if I did it successfully, though.
Also noticed the ground connector mounted to the driver's strut tower is looking quite corroded, could this also be a possible culprit?

TL;DR - car stumbles suddenly with flashing cel, check + clear DTC, idle + power return to normal...returns after a few drive cycles, without any other codes.

Hoping for some kind, wise gurus to point me in a direction 'cause I'm stumped!
Sorry guys, I've never posted like this, I just don't know where to turn...
 
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2003 protege 5
I think you're on the right track with cleaning up the grounds and checking for unmetered air. check the accordian like hose for the intake. Those can crack at the seams and make it hard to see so you might have to check it closely. Next, when is this happening? at startup? After you have driven it and the engine/underhood is warmed up? It could be the coils starting to fail once the underhood temps get hot causing the coils to start failing. Does your car burn alot of oil? It could be fouling the plugs on start up and once its warm and the oil is burned off the plugs it runs smoother. I think maybe a tune up with plugs, wires, and new coils should take care of the issue and tell you a bit more about your engine too.
 

pcb

The Diagram Dude
:
2002 MP5
Here's a good thread about coils...

Thread 'Sudden P0421 within the past couple of days; today P0302, rough idle and flashing CEL' Sudden P0421 within the past couple of days; today P0302, rough idle and flashing CEL

Coils for our car are a real PITA.
(I've got a P5, but it's the same 2 liter engine. )

If you get new ones get good ones.
Cheap ones have been know to be bad right out of the box.

Hitachi are quality coils.

20210920_200656.jpg
 

pcb

The Diagram Dude
:
2002 MP5
You can spray around your engine bay with carb cleaner to find an intake air leak. When the engine revs up, you found the leak.
 
I think you're on the right track with cleaning up the grounds and checking for unmetered air. check the accordian like hose for the intake. Those can crack at the seams and make it hard to see so you might have to check it closely. Next, when is this happening? at startup? After you have driven it and the engine/underhood is warmed up? It could be the coils starting to fail once the underhood temps get hot causing the coils to start failing. Does your car burn alot of oil? It could be fouling the plugs on start up and once its warm and the oil is burned off the plugs it runs smoother. I think maybe a tune up with plugs, wires, and new coils should take care of the issue and tell you a bit more about your engine too.
happens regardless of temp. sometime blipping the throttle makes it go away, if you clear the dtc, misfire goes away until next drive cycle. idle rpm seem low, seems like a valve is opening and letting in unmetered air. when car runs fine - no whistle from intake. replaced egr and VTCS valves(x3), coils, plugs.
 
Thanks guys, replaced all parts suggested, seems like new coil/wire/intake boot did the trick and finally set readiness! Thank you to the Gurus that could help out, I really appreciate it! You Mazda guys rock:cool:🤙
 

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