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I have a 2006 Ford Ranger 2.3L . For some years now it has exhibited stalling at idle very intermittently, and only during the summer months June-August. Replacing the IAC valve sometimes fixes the issue for the rest of the season but sometimes I will have to replace it twice. Usually turning off the engine and then restarting it will allow the idle to return to normal but then, seemingly randomly, it will again die at idle. Runs fine off idle. No trouble codes have ever been thrown. Unplugging the IAC causes the RPM to drop dramatically. I just recently installed a Motorcraft IAC and the truck ran fine for about a week and then I came to a stop at an intersection and sure enough it died. I restarted it and it idled fine until I got home. Also, it does not stall while the engine is warming up, only after it has reached normal operating temperature.
The first thing I would do (after checking for codes and freeze frame data) would probably be to clean the throttle body.
It's free, easy, and cures most of the "stalls coming to a stop" complaints I see.
The IAC is only allowed to open so much to keep the car running, if it's compensating for a dirty throttle bore, there may not be enough left to keep it running when it needs it.
Thanks for your response. I did clean the throttle body last summer (had to use high quality brake cleaner because MAF cleaner wouldn't do the job). I did notice some carbon build up downstream in the manifold but did not address that. When I installed the new IAC I inspected the throttle body again and it looked pretty clean still. I also inspected the air filter and used some MAF cleaner on the MAF sensor. I should note that the truck has 200K on it, but I keep it well maintained and the issue has been occurring for the last 40-50K. It almost feels like one of the sensors is sending a glitchy signal to the either the ECU or directly to the IAC. But why only during hot weather and why so intermittently.
Finally was able to catch it misbehaving while my Forscan setup was connected. Looks like the IAC, which is supposed to go from "Preposition" with open throttle to "Dashpot" with closed throttle on deceleration to "Ctrl Learn" at idle, is getting stuck in the Preposition mode. A restart immediately resolves the issue so I'm not sure its a problem with a physically stuck IAC. It also is very intermittent (it's been a month since I last posted). Any ideas?
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