Stall in summer only after driving for a while :(

Hello Ladies and Gentlemen,

I have a Honda Civic Hybrid 2005 that I drive fairly regularly. I keep up with all the maintenance never had a problem… That is until last year. In the heat wave of Northeast 2012, the car started stalling after long drives. It only happened in mid to late august when temperatures started reaching the 90’s. In the fall and winter the problem went away. I took it to the dealer in around October and they could not reproduce at first then later came back to tell me that it was the IACV valve and said it would cost about 700 dollars for the fix. It promptly went away for the entirety of the winter and has now returned in june. As far as I can tell it only happens in the heat when you are idle after driving. It appears that the RPM’s go to low (400<) and the thing stalls…

Has anyone ever heard of anything like this? How did you fix it? Can I do it myself? Where the hell is this IACV maybe I can clean it out or something?

Any help would be appreciated,

I don’t have experience with hybrids, but this could still apply since your concern is about the gas engine in your car. IAC usually means “Idle Air Control”. The “V” presumably means valve. Its purpose is to control the idle speed for the various operating conditions. It does the same exact thing as you pressing on the gas pedal. But automatically. For example, when you first start the car in the AM you probably notice the idle is higher than normal, then after a few minutes the idle speed drops. This is the IAC doing it’s job. On a 2005 I expect the ECM monitors the coolant temp, and when it heats up, it tells the IAC to drop the idle speed. But it could be overdoing it, dropping the idle speed too low on hot days, in which case something or another needs to be fixed. It could be the IAC itself, or it could be some other problem unrelated to the IAC, like a faulty O2 sensor or leaky fuel injector or faulty coolant temp sensor. It could be the ECM itself is on the fritz. Since it happens on hot days, that implies the fuel/air mixture could be too rich, which could possibly cause stalling.

The Idle Air Control Valve controls the engine idle speed whenever the accelerator is released.

One way to test for this is, the next time you’re pretty sure the engine is going to stall, with your left foot firmly planted on the brake pedal, with your right foot slightly tip into the accelerator. If doing this prevents the engine from stalling the IACV is being effected by heat and probably requires replacement.