02 Protege Random Cylinder Misfire

[paqman]

Hey guys. Working on my in-laws 2002 Mazda Protege. It is chugging heavily at idle, nearly dying, but never does. It only happens at idle. Driving seems to have no issues. It also only happens after the engine is slightly warm, (1-2 minutes).

CEL gives a P0300 (random cylinder misfire).
Replaced new spark plugs - no change, still chugging.
Replaced ignition coils - no change, still chugging.

At this point, I cleared the CEL, drove it around for a bit (but not long enough for the CEL to come back on). Pulled codes again, this time a "pending" code came through, P0301 (cylinder 1 misfiring).

Does pending mean that it hasn't had enough time to test it thoroughly so it only has noticed cylinder 1 misfiring right now, and it may soon register that others are misfiring as well? Or is this a good indication that the ignition coils (which have built in plug boots/wires on them) fixed the misfiring on 2 of the other cylinders and now it really is only cylinder 1?

So to clear it up a bit, see the picture (not actual engine). You can see that cylinders 1 and 3 have just the cables going on the spark plugs. Cylinders 2 and 4 have the ignition coils with spark plug boots right on them. So effectively, the spark plug boots have been changed on cylinders 2 and 4, but not 1 and 3.




Do you think there's a good chance that putting new cables on 1 and 3 will clear it? I know, it's a cheap, easy fix, but they live far away, and I don't get over there very often, so I'm trying to troubleshoot as much as possible so I can go over there ready to fix it.

Any other ideas about this problem?

[sixpix]

I'm having similar symptoms on my 2002 Protege but I also got a P401 which is insufficient EGR flow per the Autozone guys. I'm planning to check the EGR for restrictions tomorrow. If you find anything please post.

[paqman]

Originally Posted by sixpix

I'm having similar symptoms on my 2002 Protege but I also got a P401 which is insufficient EGR flow per the Autozone guys. I'm planning to check the EGR for restrictions tomorrow. If you find anything please post.

Yeah I've heard about the P401. I bought some new plug wires for cylinders 1 and 3 (seeing as 2 and 4 are already replaced). I'm going to put them on tonight when I'm at the inlaws and see how it goes. I'm hoping that fixes it. I'm tired of giving them bad news, plus, that would be a great mother's day present for my mother in law.

[sixpix]

Took the EGR valve off today and found the shaft was sticking. I cleaned it by filling it up with brake cleaner and then pushing the shaft in and out. Eventually it started moving freely. I oiled it and re-installed it and the car is now idling smoothly. At first the idle was high but eventually came back down to around 800 rpm. So far, everything looks good.

[paqman]

Well, it turns out that was the exact problem with this car too. Only I couldn't see a way to get the sucker off easily without taking the manifold off. So I just let them take it to the dealer. They determined it was the EGR valve as well, but obviously they're not going to clean it and put it back in, so they put a new one in. Ran her about $400. I'm sure if I had an entire saturday morning I could have gotten it off, cleaned it, and put it back on, but I'm not that nice. Oh well, it fixed the problem.