Hi all, and thanks for your time. I have a '04 Ford Mustang Convertible, V6 engine, and today on the way home it really scared me. I was stuck in traffic for an hour and a half, moving a few feet at a time, when all of the sudden, about 40 minutes into it, the RPM’s dropped almost to the point of cutting off. This happened a total of 3 times until I finally got out of traffic. The last time it happened, I threw my hands up and said “I am going to see what it does.” The previous 2 times I had stepped on the gas, but this time I did not, and it got to the point to almost cutting off, then caught itself and throttled back up.
Now, it was 90 degrees in Charlotte today and the AC was on. I was told this might be the issue. I have never had this happen before, but then again I don’t live in Charlotte and this was something that has only happened this once in the whole year I have owned it. I thought maybe I was low on fuel, but the gage did not register as low, and no fuel light came on. I am hoping it was just the AC compressor driving the RPM’s low, but I would like to know what you think.
It could be a host of things. Since you’re confident the gas was not low, I’d suspect some temperature related issue. Did you notice if the engine coolant temp was in the overheating range? If not that, probably something in the ignition system is starting to fail. A coil or a cam or crank sensor would be the most likely. Is or was the check engine light on?
The IAC valve is a stepper motor that allows air into the engine under different idle conditions. And when they get hot they can fail to go to the proper position for the idle condition. The engine can then start to idle roughly or even stall.
One way to check for a Ford IAC valve being effected by heat is, with engine up to full operating temperature, take the handle of a srewdriver and rap on the IAC valve with the engine idling. If the idle speed changes replace the IAC valve.