Random misfire on initial start up

Unit is a 2000 3.4 l Having a issue when starting it up first time everyday happens when sitting for a day or so happens only on the first time. it starts ok, but misses for 30 or 45 seconds then smooths out fine. and doesnt happen again , until it sits over night.it does it on cold or warm days. more often in cold, has only set a code one time. and it came back as po300 random misfire ,so pretty much eliminates a bad injector, since a random miss fire, plugs and wires fuel filter are good fuel pressure seems fine. i cant find anything obvious, my cheap scan tool has only came up with the one time code po300. have cleaned the throttle body maf. unable to locate anything on a cold start injector for a3.4l like on a 3.0 l. any suggestions it not a terrible issue, as it only occurs on first start .but i wish to cure it now before it does,its becoming more annoying and i am hoping to find a answer here. because i now have time constraints that wont allow me the time to really dig into diagnostics i am capable but my ol lady became very ill and leaves me virtually no time .please if anyone has reliable info that might help or has come accross this issue any advice would help thank you in advance

 

Does it use any coolant?
Does it “flare” on startup? For example, rev to 1500 or so then come down to 1200 or so cold, or 700 or so hot?

 

My '03 Tacoma is doing the same thing but it only happens once in a while more so when it's hot. I have pulled up to a red light and it has stalled out. I crank it up again and it miss for a few seconds, then smooths out after hitting the gas a few times. I've already changed the spark plugs and all three coil packs to denso

 

Generally not a good sign as it can be a failing head gasket. Been there, done that. Rent you a chemical block tester from your auto parts store to rule it out.

 

I had that code last year. For me it was coolant leaking into the cylinders. Went on for about 6 months or so. Head gasket job did the trick.

 

I did that to mine and it passed. Fluid stayed blue.

 

It rarely works in this scenario, usually for the chemical reaction to happen it needs a mega leak.

I use the coolant funnel as a pre-diag, I watch for combustion bubbles in the coolant.

 

I think I remember reading something about that. Sometimes you can get a false negative with a block test.

 

After you shut it off for the night and it cools down loosen the radiator cap but leave it on the “catch”. In the AM see if it misses with no pressure in cooling system overnight.

 

Going to put a bet on head gasket here. Experienced the same thing for several weeks with my 2.7 3RZ. Would advise pulling the plugs after it starts up like that and see if any are irregular and borescope to see if one of the pistons is cleaner than others.