The symptom: while accelerating, at a very particular throttle level/pedal angle my engine recently started whistling in a very high pitch. If I let go of the gas or push it in more the sound goes away.
I said that this is new. To be more exact this started happening after I was diagnosing something else and did two thing:
- I lowered the idle, which was too high
- I checked for vacuum leaks using carb cleaner all over the intake system while listening for any change in the idle. Nothing was found.
Is it possible that I have an air leak that I haven't found? If so, is there a (better) method of checking for vacuum leaks that will allow me to find a more subtle leak, that might not show itself when using the carb cleaner method?
Also, is it possible that the whistle is absolutely benign and I'm worrying about it too much? I cannot seem to replicate it while the car is standing still, it seems to either need load on the engine or moving air.
I am driving a 4 cyl 1993 Acura Integra, no turbo. About a year ago I replaced the stock intake with a cold air intake (the noise is new, however).
Update: I tried to check the PCV valve and it crumbled in my hand. In the process of replacing it. Hopefully that's what it was.