Got a CEL yesterday, can't seem to figure it out. Here's the story ..

I swapped valve covers in the morning so I could work on repainting my old one, and after about 10 miles of driving with the new valve cover the car started to sputter and idle very low. At first it only happened when I had it in Reverse or Drive, but not in Neutral or Park. I'd come to a stop and it would sputter pretty bad with the idle going down to about 400-500 RPM. It never died though, only sputtered. Car drove fine and shifts as smooth as always, but just today started to sputter very slightly while driving also. Problem is most obvious when I'm at a stop. I really don't know if and how the new valve cover could have an impact on this but that's when it started happening.

So today I began my troubleshooting, and first thing I did was pull the CEL code. Turns out it's P0300 (random cylinder misfire). Did some searching on here and found it could be a number of different things such as air/fuel filter, MAF, PCF valve, EGR, bad coil, or vacuum leak.

So far I've done the following:
1.Changed air filter with brand new unused Simota filter
2.Inspected MAF for dirt and such, and it looks brand new
3.Checked spark plugs, replaced with new NGK's
4.Searched for a vacuum leak but everything is in place
5.Checked PCV valve, replaced with new one
6.Replaced the sensor on the bottom left side of the valve cover (dunno what it's called)
7.Just for fun, checked all the grounds and made sure the battery terminal was secure

I went to a couple Auto Part stores in search of new plug wires and coils, but had to order both. They'll be here Wednesday morning and I'll see if that makes a difference. If the new coils/wires don't fix it, I'm gonna try cleaning the EGR valve again, but if that doesn't fix it then the only other thing to check is the fuel filter. Anyone know where I can buy one, can't find one anywhere (local or online).

Also, anyone have any other suggestions on what I should check out? I'd apreciate the help, I'm dead without my car ..

 

Wow, you've been pretty thorough. But it's gotta be related.
What about the electrical connections on the coil packs? Are they all in firmly?

 

Yes, all connections are firm and double checked.

Another thing to add that I just noticed recently is that my exhaust fumes smell like sulfur really bad. Kinda like rotten eggs actually, it's pretty stinky!! Could it be o2 sensors?!? I don't think o2 would cause sputtering of that sort though would they?

 

Idling problem's fixed now, turned out to be bad plug wires. I don't know why I didn't figure this out sooner but I took a second look at the plugs I took out and noticed the two plugs that have the wires going into them (1&3 from the left) were in pretty bad shape -- see pic below. I dunno if it was the wires or the Iridium plugs .. I think it might have been that I was using Iridium plugs in something that really didn't need them, so it was probably the combination of both.




Anyway, now that this problem is gone I wanna take care of the stinky exhaust. As I said before, smells like rotten eggs and I noticed it before too it's just that now it's gotten a lot worse. What should I be looking into? o2 sensors, maybe a clogged cat, I dunno .. I really don't know.