Car overheated from a seized thermostat and then blew the headgasket between cylinders, no oil or coolant mixing happened. Thermostat and headgasket have been replaced and compression is back to 180-185 on all cylinders. Car runs perfectly fine during warmup. Once warm, the car wants to die, and keeps nearly cutting out, but then recovers, entering a rhythmic surging. There was no sign of this beforehand.

If I unplug the MAF to run the car in open loop, it also runs perfectly fine when warm.

I have checked for vacuum leaks and found none. I have bled the coolant system. Any ideas?

 

Maybe try replacing map sensor??

 

Make sure you burp and bleed the coolant system properly, an air pocket at the idle air control valve can cause similar issues

Depending on modifications its also possible to mix up the front oxygen sensor connector and rear oxygen sensor and plug them in backwards

 

Im having issues with my iacv as well. Please explain to me what exactly these coolant passages in the iacv are for. I've been told by some that they are only there to prevent freezing in cold weather, but then I've heard that air pockets will effect operation of the iacv. If you take the iacv off you will see that the coolant passages run to nothing and basically just loops the coolant back out. So how could air pockets effect operation of the iacv?? Then again, why are the passaged even there?? There is no water in the iacv, nor any temp sensors, so how could it freeze to begin with?? Understand I am not questioning your knowledge of how the iacv works, it's just that I want to fully understand it to help resolve my own issues. Also, could running my iacv without the coolant lines hooked up to it cause my iacv to malfunction, even in above freezing temps???

 

The idle air control valve has coolant flow through it so that the air density is adjusted for the engine temperature to produce a more stable idle.

When the air is hot it is less explosive, less dense, this can cause the car to idle lower. When the air is cold it can cause the car to idle higher. If the ecu senses the idle is higher than expected based on map sensor and coolabt sensor readings it will send a signal to the idle air control valve to get a response from the engine. If the response in idle is not what the ecu expected the car triggers a check engine light

Long story short honda designed hot coolant to run through the idle air control valve so that the car would have a more stable/predictable idle. Hotter air is easier to regulate because it is less dense and causes a smaller reaction when allowed into the intake manifold. This allows the car to idle exactly at 750rpms (or whatever it is) and not just a random rpm every time

So yes hook your coolant lines back up. The ecu expects hot air to come in from the idle air control valve based on coolant temperatures

 

Ok, will do. Thanks for the knowledge!