Practically every time I start driving in the morning l hear a loud vacuum noise from the front. I also struggle to move forward it seems. These symptoms only last until I take my foot off the accelerator after about 50 feet, then vanish. After that it runs great.

It’s a ‘97 SD, Automatic.
I’ve cleaned the MAF and throttle, new IAC valve, air filter, new breather hoses. I’ve checked for vacuum leaks and found nothing. Can’t figure it out!

 

Describe in more detail the vacuum noise and where specifically it is coming from. When you struggle to move forward, you mean during acceleration or just the foot off brake?

 

Vacuum leaks can be hard to find. My manual recommends removing the fan belt to eliminate other noises for a short test engine run (cold). Maybe the noise could be the fan clutch or power steering or tensioner, for example. Or maybe the belt is slipping.

 

I hear the noise coming from under the hood, in the left side. I can’t pinpoint the noise specifically because it only happens on the first couple presses of the accelerator, and I’m inside.

I can only describe it as a ‘vacuum noise’ because it doesn’t sound rough, like an overworked engine, or like an exhaust noise. It sounds like a vacuum you’d use to clean your carpets. Maybe I’ll need to provide video.

Also, on initial start up my idle is about 1300 rpm, after a few miles it goes down to 700 rpm. It feels as if the truck has to clear something out of itself that’s built up before it runs normally.

 

Is the A/C running during the noise? These trucks make a loud fan roaring sound when the A/C is on. Fan clutch maybe? i took mine out and cleaned it without having to replace it.