Toyota 3.4l p0300 Only After A Hot Start. Goes away with blip throttle. Help?

Here is the deal.

Toyota 3.4l 2001. When starting truck hot sometimes it runs rough for first 30 seconds right off idle if you don't blip the throttle. It will set a check engine code if you let it really stumble. p0300.

You can get it to not set this code by just blipping the throttle as you start it after it is hot. Does not have problems starting cold.

I am leaning toward a fuel delivery problem or injector.

Anyone have experience with this? Truck has 366,000 miles on original engine. Doesn't use a drop of oil or burn antifreeze. I have replaced the plugs recently & done the 4" deck plate mod. Problems did not start immediately after doing either one of those.

 

Howdy,

Few things you could try, remove and examine the spark plugs. If they're new then it'll make diag easy (hopefully). Did you confirm gap on the plugs? Did you get the iridium plugs like toyota calls for? It makes a noticeable difference.




Ever changed the fuel filter? Run injector cleaner?

 

P0300, random multiple cylinder misfire. From the symptoms you gave it sounds like one or more of the injectors might be seeping after you shut her off. Dual electrode plugs or something else.

 

I was leaning towards a seeping injector.

Anyone have any ideas on how to diagnose this? I keep seeing people saying they replace injector #2, but I don't want to just guess, or I will just 6 new ones in. I just don't like shotgunning parts unless I have too.

I also just cleaned the MAF with sensor cleaner. No Change.

As far as spark plugs I recently changed them 6000 miles or less, I used dual electrode toyota OEM plugs. i did not gap them as they are not to be gapped from my understanding. I used dielectric grease on them, and the truck pulls great when you step on it.

 

While it's true you don't set the gap, never hurts to check they are properly set.

Seeping injector is possible, but I've heard very little issues with these injectors. Could have them tested to confirm.

 

if this is your only vehicle your options are limited due to the time it takes to check some things out. An easy way to check for a leaking injector is to take the spark plugs out and let it sit. Take a drinking straw that is still in the wrapper and stick it into the spark plug hole at the bottom of the piston where gas would settle and swish the straw around and pull it out and sniff... if it is wet and smells like gas you found one... flip the straw around and go to the next hole.

 

Not sure I agree with the "lean" diagnosis on the picture, mine look almost like that and many other sites will say a thin brown coating is okay. If there is white residue on it, you are definitely running too lean.

Here's a conflicting picture.




This is the chart I like (below):


Many sources say the red deposits are a result of fuel additives, which are pretty much in most gas station fuels now.

 

Any other advice for p0300? Could it be fuel filter? my truck does have 366,000 miles or a losing pressure fuel pump?

 

I would say leaky injector, especially if it only does on hot start. If you have a bore scope you could check.

 

Not sure if you found your problem, but I had the same code. I found I was sucking antifreeze into the intake manifold on startup and causing the code. When the engine was hot it just burnt the antifreeze and ran fine. Look for loss of antifreeze or white smoke at cold startup. It could be a bad gasket or cracked antifreeze pipe which is under the plenum. I just put a stop leak product in my rad and the problem went away. With 325000km on the engine I wasn't about to spend a lot of money tearing everything apart.