2002 Protege5 with Random MRisfires galore
I've been reading this thread a bit and want to see if anyone has any ideas where I can go next in my troubleshooting basically the same issue. I'll sum up what I've done here:
Car cruises fine, than power drops like a rock (feels like 1 or 2 cylinders just stop firing), then clear up 20-30 seconds later. Sometimes it'll do it cold in the drive way, and sometimes it has to warm up. Also, it'll some times go a day or two with no issues and then be practically unusable for a few days. Lately once it's warm it might not even clear up and today it wouldn't even let me restart it once it stalled due to the issue. (I eventually did get it started after playing with spark plug wires for a bit)
I get P0300's and sometimes P0421's.
I swapped both coil packs, put in some new Platinum +4's (though the old ones were still gapped and clean, it had been about 80k since then). Put on new spark plug wires, replaced the top O2 sensor and ECU. Cleaned the EGR Valve, did a sweep check on the TPS and cleaned/sanded all the grounds on the driver side strut tower.
All these things made some sort of impact, it seemed at the time, as things would run well for a week or two afterwords before returning to the same issue (well, besides the sweep check since I didn't change anything).
I did notice for a few weeks that if the car started to sputter, if I wiggled the wires going to the passenger side coil pack, it would miraculously run perfectly again. Figuring I had solved the issue (and because I couldn't find a replacement wiring harness), I spliced new wires into the harness a few inches into the split loom and soldered them right to the coil (If this worked I was going to drive an hour or two to a boneyard and try to get a replacement as the wiring harness from Mazda only comes in 1 size, at $1200.) And like other things it seemed to, for a week. Week's over, now it seems like #3 (same coil pack, the one with the spark plug wire to the side of the coil) doesn't want to fire, sometimes... I actually swapped the old plug wire back in and it worked for a day. Then, back to the same.
Any other ideas? I checked vacuum lines, replaced a number of them 'cause that's a $3 fix I figured couldn't hurt. Thought about maybe the fuel pressure regulator, but it seems that it's mostly #3 now that's got the problem. And it's not that it's just misfiring, if it's stuttering and you pull the spark plug wire from #3, it makes absolutely no difference, like it's not even getting spark, but you can smell that it's getting fuel that's not burning.
Sorry for the novel, I've been at this for a while it seems... Thanks for any help!