05 Tacoma 4.0 PO300 code.

Hey folks, I did a search for this issue on here, but nothing directly related populated. My 2005 Tacoma with the 4.0liter engine when I start it cold, only the first start of the day it will run a little rough and sometimes log a PO300, but not all the time. Once it runs for 30:seconds no issues, I can drive it all day and start and restart it and it never acts up. I have ruled out plugs and coils. I have read some forums and they say head gasket. But I am not using coolant and it doesn’t smell like coolant when it runs rough. It’s just not bad enough to set a specific cylinder code yet. If anyone has had this issue specifically please let me know. I love this truck and have had it since 09. Thanks in advance for your help.

 

If it’s not coolant, maybe a leaking injector?
Have you checked the coolant in the radiator?
The reservoir isn’t a good indicator.

 

The symptom sure sounds like a possible headgasket failing, the best check is to pull all the plugs and pressurize the cooling system with a pressure tester. Let it sit with pressure on it for a few hours and then look in each cylinder for coolant.

 

I thought this as well. So when I was replacing my leaking valve cover gaskets and had the upper plenum off, I ordered what I thought was a “set” of injectors which what was it called it on Toyotas website for 138.00 I thought that’s worth it. Then parts arrived and it was 1 injector with seals on it. . I always referred to a set as ALL of something, but not Toyota. So, rather than guess which one it may be, I didn’t install it yet, as another 700 bucks to replace all of them for a guess is just not feasible at this time. Being I am not using coolant, and radiator is full, this was my thought as well. I’ll keep this thread updated once I figure this out. Thanks for the quick response. Have a Blessed weekend my friend.

 

Good morning, I will do this, as it had crossed my mind, reason I have not yet is coolant system pressure is higher when running, so why wouldn’t it be worse or be using coolant then? I’m going to do this today and will update tomorrow. And thank you, for the helpful links you have on your response, I am considering buying a tool with a cylinder misfire graph, so I can watch it when I start the engine to determine which cylinder is acting up. But I’ll hold off unit the coolant system leak down test is performed. Have a Blessed weekend my friend!

 

Are you checking the coolant level cold, before starting the engine? In both radiator and expansion tank?

 

good afternoon, yes checking both when cold, as the level rises some in the expansion tank when it gets hot. Thanks again folks, can’t wait to update you with my findings!

 

Even with no visible coolant drop, it still is very likely a headgasket.

The pressurized coolant mists into cylinders overnight and causes a misfire in the morning.

You could try to get it roaring hot, park it. Then in the morning before starting it, remove each plug and inspect the cylinders for liquid.

Traditional headgasket checks like the chemical don't work on these really slow leaks.

 

Update on my issue. I have confirmed it’s a head gasket unfortunately. Now, the questions for you good folks that helped determine the issue. My 05 Tacoma 4X4, quad cab, long bed has 230K. Do I fix it, or trade it in on a new one? I have the ability to fix it myself, just wondering your thoughts folks. I appreciate your time and feedback. Have a Blessed Sunday.

 

Even an older tacoma is still worth fixing in my opinion. Especially if you can do the work yourself

New trucks are crazy expensive right now

 

Tore the engine down yesterday afternoon. Man, that’s a lot of work. Glad there was a YouTube video with some important information given. Now, to clean up all parts up and generate an extensive parts list.

 

It was blown between the cylinders, wasn't it?

Don't forget to replace that stupid plastic water bypass tube with a metal one while you're in there.

 

4.0L doesn't have that, that's on the 2.7L.

 

Just wanted to send a huge thank you for all the help getting my Taco sorted. I finished the head gasket repair and after a little hiccup it’s all good! I did invest in the factory service manuals, and I am so glad I did. They were Super helpful, and with the step by step instructions it kept me from overthinking and becoming overwhelmed. This repair looked a lot easier on the YouTube video for sure. But, after several nights and one long weekend, she is running like new. Now to get some new tires on her. Thanks again to all.

 

I’m glad it worked out. I did mine last year and she is still running great.

 

Can you link the youtube video so I can watch it?

 

https://www.youtube.com/watch?v=pIb...uMCBsaXRlciBoZWFkIGdhc2tldCByZXBsYWNlbWVudA==

I have never copied a link from youtube. if this does not work, Go to youtube and type in toyota 4.0 liter head gasket replacement. it will come up as a tundra, but its the same 4.0 liter.