Started with a P0305 and now P0300
 

Okay here we go. My 2004 D2 has 88k on it. Changed the plugs when I did Disco Mikes service. New 8mm Magacor went in the also. All of a sudden yesterday it started to stutter up a hill the CEL came on and then my ultra guage started chirping. Came up with a P0305 code. I pulled the plug (bosch plat 4's). It looked okay, a little whitish. Wanted to replace just the one, ended up replacing all becasue my local shops did not carry. Replace it with Bosch platinums.
Same problem is happening (occurs under load), now it is throwing P0305, and P0300. Any thoughts from the esteemed panel out there?:(

Try swapping plug wire 5. Try looking it over under blacked out dead of night conditions looking for any arcing. P0300 is simply multiple misfires.

Do you mean swap the wire out? I guess that begs the question of getting one to the coil and finding a single wire. I will check for arcing as soon as it gets dark enough here

As you well know, moving wires about on the coil packs is for elves with tiny fingers and lips glued shut to prevent propagation of profanities.

Savannah
Did discover a little arcing on number 5. Took plug out checked gap, and reinstalled. Took care of that issue but still throwing a P0305 code. Not going to try wire swap at this hour and I dont have an elf handy.

You might want to make sure the spark plugs porcelen is not cracked, also verify that you did press the coil end of the #5 wire all the way onto the coil.

Will check as soon as I get a chance Mike. One thing I forgot to mention was that about 4 months ago, it threw a code for lean engine in that bank of cylinders. Only happened a couple of times, then went away. As far as I know, these are the original O2 sensors. Correlation there somewhere?

I had a similar issue few years ago on my dads truck. Think the exact same codes.

My first coarse of action was like what you've done, swapping plugs/wires to see if the miss followed. It didn't.
I was then going to start looking at the coil packs and injectors, but then the P0300 showed up and made me scratch my head.

As a last ditch effort, I dumped some injector cleaner in the tank. After 2 treatments of the stuff, the codes have been gone ever since. I think maybe it was a bad tank of gas.

So, you can always give that a try.

As for the lean codes, if they continue to pop up, first thing i would check for are vacuum leaks

The bad gas is an interesting idea. I filled up at Costco the other day, perhaps that is it. I put a can of Seafoam in the tank so we will see if that helps to clear it up. Bit of a catch 22, as I am reluctant to drive the car very far, so emptying the tank may take a while. The lean codes have not reappeared for a long time.

I also should have mentioned, i tried seafoam in the tank at the onset of the misfire, and it did nothing. I think there are better fuel additives out there. Techron, BG 44k etc..

The one i used after was a Canadian Tire branded one, i don't know who makes it, but it worked good.