sounds like a early stage of a head gasket failure hence the misfire only when cold, a failing fuel injector would be more predominate. When you let it sit over night as the coolant system depressurizes coolant drips into the cylinder and causes a misfire/stumble at cold start up and clears up. Have you kept an eye on your coolant reservoir and noticed it lower than usual?

I just went through this a few months ago. Look at the coil packs.

You are local to me and I've seen your truck at the truck shop. I have extra injectors if you want some to swap out for trouble shooting purposes. We can also swap the coils off my truck, they only have about 8,000 miles on them. My old ones with 260,000 tested "fine" but the new ones fixed the problem immediately.

Man, i sure hope it's not a HG. I'm never low on coolant though, it's always at the top of the radiator. I'd have to check the reservoir to see.


This directed to me? If you're in socal we're not all that 'local' haha.

This was pre coffee. LOL

Did you ever sort this out?

Curious as well. I still think your ride hated being stuck in that Arkansas gorge or stream some years back and is exacting revenge on its driver.

I did get it fixed up but I'm monitoring it as of right now. I had 6 OEM injectors pulled from a local yard here and had them sent off to be professionally inspected, rebuilt/cleaned. Got them back and swapped them in. Also redid my valve cover gaskets as it was apparent they were leaking at the back (due to me not using any FIPG per the manual).

The spark plug on Cylinder #3 (where the misfire was) was not fouled and in fact, still look new (less than 20k miles on it anyways). The wire to number 3 coil pack was a little dirty as was the coil packs contact point. I cleaned them both up the best I could and put #3 coil pack at the #1 cylinder position.

As of right now, the start up is normal and no longer giving me issues. If after time It begins to do the same thing I'll know for a fact it's not the injectors. If it's cylinder #3 misfire it's the wire and if it's cylinder #1 misfire it's the coil pack. I think I'm due for new wires at this point anyways, so I plan to order a set soon.

lol, the elevation definitely plays a roll in it's every day behaviors now. I rarely ever got over 3k on the tach down south. Here, it's an every day occurrence.

At least it is the easy stuff so to speak. When my Denso replacement wires went south on me last Jan due to a hole in the #4 boot I replaced the wires with OEMs that can sometimes be found on Amazon for $40. Also replaced that coil and have had no problems since then.

I had a cel indicating an intermittent miss on #4. When i changed the plugs and wires, I found a broken wire end. The boot shows some arcing. Plugs had 35k
on them, i think the wires were original. All issues seem resolved.
Sorry, having trouble sending pics.
Dick

Well I got a rough start up this morning and a couple codes, P0300 & P0303 is back

Unfortunately, I think it's the worst case scenario at this point.

So far:
- Replaced Injectors
- Replaced Plug Wires
- Swapped #1 and #3 Cylinder Coil Packs
- Check #3 Spark Plug (looks new)

So my next guess is burnt valve. I'm going to switch around spark plugs first, then I guess if that doesn't fix anything I'll have to look into a valve job.

my guess with the miles is fuel pressure issue. check so its proper before you spend more $$$.

Compression check and leak down test. Maybe have fluid analyzed. Good luck.

Thinking about it usually of a burnt valve you will constantly have an issues. Usually at WOT and higher rpm. Get a major stutter/misfire. I also never got a cel since coil plug and injector was all firing. Different vehicle though.

Compression test is next on the list.

It's a very weird situation. I did a block test a few weeks ago and it came back normal. I dunno what is up with this thing. But will keep troubleshooting.

It drives normal once it gets past the rough-ish start.

Could a belt or pulley issue cause a misfire in a specific cylinder? I'm getting some nice screeching in the morning along with the (sometimes) "water faucet" noise. Clears up after only a few seconds, but it's worth mentioning.

How is your 4Runner now? I am experiencing similar issue.

I was driving home one evening and the engine almost completely let up. It was losing compression, backfiring, and stumbling. Long story short, I ended up replacing the engine. Took the old one apart and it revealed that #3 cylinder was completely washed with coolant due to headgasket failure.

My best advice, do a leakdown and compression test if you've crossed off all other possible causes.