Cold start issues

Hello everyone. New to the forums and also new to the Tacoma world!

I’ll try to keep this as short as possible- I am currently having cold start issues with my 2.7l manual taco that I’m really hoping someone can help me with.

the symptoms I am getting are as followed- When I go to start engine first thing in the morning (coldest I will ever see is about 1 degree C.) the engine will fire up with no extended crack, always fires up right away. When the engine fires the first about 2 seconds the engine will climb into “cold idle” so roughly 1300-1500rpm. About 2 seconds after that it will immediately drop to about 800rpm, the engine will stumble for about 5 seconds then it will smooth out, but still “cold idle” at only 800 rpm. Its like it wants to cold idle but something is stopping it. Aside from the 2 seconds of rough running and the low rpm cold engine idle, it runs perfect. Only code it will throw is p0420 (cat issue) which in my opinion should have nothing to do with cold start.

here is the list of things replaced/tested. New idle air control valve, new ECT, new MAF/IAT, new thermostat. I have verified there is absolutely no intake leaks. I’ve pulled the EGR valve and verified that the valve is opening and closing properly. I have verified that the EGR vacuum solenoid is working as it should, I have verified all live data readings are within spec. I’ve pulled and cleaned the throttle body, I’ve done compression test and leak down test and both passed. I’ve done battery disconnect, cap discharge, multiple drive cycles to attempt to learn some values. The only engine mods are cold air intake and Manifold back exhaust.
I’m completely stumped and am so tired of throwing parts at it. Please! Anyone with experience with this please chime in!

 

Heavy carbon build up can cause this, and is more likely on an egr engine.

My next step would be an intake clean with seafoam or something similar.

Ideally you'd pull the intake manifold and look at runners, but it's simple to do an intake purge and not a bad idea to do.

Big thing is make sure its operating temp, and drive the snot out of it after.

You sound mechanically inclined so you likely know how to look it up.

My 2c

I don't work on a lot 4 bangers, but a fuel pressure drop off can cause this as well, not as common, but possible. FPR or pump are possibilities.

 

Ahhh deadly! That’s actually something I haven’t tried! I do have access to intake/fuel system cleaner so I will definitely give that a shot! Appreciate that!