Loud wheeze tone at Intake on hot days.

[PNWADV]

Hey folks, I have a 99 Ranger 4.0L, manual trans.

I've owned this truck for 4 months, and during that time Portland OR has had 2 days over 80 degrees F. On those two days I drove to work in the morning (below 80 deg) and had no issue. When I drove home in the afternoon I heard a high pitched wheeze sound just as I pulled into my drive way. This has happened two times. Each time the conditions have been the same. Hot day, 30 minute drive and when I hit the drive way the sound began.

The second time this happened I let the motor run, popped the hood and began to scout around to find the source. The sound is coming from the intake manifold. Specifically the sound seem to be focused at the IAC or where the EGR enters the intake. This general area is where the sound is the strongest. I have some of those stethoscope probes and I listened to many spots on the motor and those two areas were the loudest. The EGR itself did not seem to be making much noise, nor did the metal line feeding it from the exhaust manifold.

I would describe it as a high pitched tone, sort of like if you tried to suck air into your lungs and hold a note at the same time. It sounds like air is trying to get past a valve but its getting restricted.

I know this issue has to do with temperature and time. I've driving this truck back and forth from work almost daily, and the only time this issue has popped up was on a hot day.

I just curious what part of the motor or emissions would open or close when the motor hits a certain temp?

Thanks for reading.

 

[RonD]

Welcome to TRS

EGR is only use after engine warms up, but also only when driving, when engine is under a load, not at idle

IAC Valve has a Vent, under a black or metal cap that can be popped off, it can make a "whistling" noise
Vent is there so valve can slide in and out without air pressure building up behind it
If the valve's seal should leak a bit then you get the noise

There is no emissions difference based on outside temp

 

[PNWADV]

Welcome to TRS

EGR is only use after engine warms up, but also only when driving, when engine is under a load, not at idle

IAC Valve has a Vent, under a black or metal cap that can be popped off, it can make a "whistling" noise
Vent is there so valve can slide in and out without air pressure building up behind it
If the valve's seal should leak a bit then you get the noise

There is no emissions difference based on outside temp

Thank you RonD.

I thought that the IAC Valve was causing the sound. When I touched it with the stethoscope I nearly blew out my ears.

I'll check that part out tonight.

 

[rusty ol ranger]

Thank you RonD.

I thought that the IAC Valve was causing the sound. When I touched it with the stethoscope I nearly blew out my ears.

I'll check that part out tonight.

For what its worth...my 460 was doing something similar and after pulling my hair out to find it i finally figured out what it was...

The throttle body was warped. Had a machine shop level it and its been fine since

 

[PNWADV]

UPDATE:
I took the IAC off, cleaned it with throttle body cleaner and a small fine pipe brush and some air pressure. Lots of carbon build up. I removed the little breather cap RonD mentioned, it was clear. I let things evaporate then installed the IAC. When the motor fired up I heard a very low level wheeze, similar to what I had heard before. I listened to that area again and realized that the IAC was making the noise. As the motor ran I removed the breather cap. The noise went away, the motor realized there was a vacuum leak and tried to compensate. I plugged my finger over the brass nipple (which the breather cap fits onto)...the motor recovered from the vacuum leak, but the noise started again. Again, I took my thumb off the brass nipple, the sound went away and the motor adjusted.

So I'm going to buy a new IAC. I'll update this thread to let others know if this resolved the issue.

Thanks to all for helping out so far.

Rusty Ol Ranger, thanks for your input.