When I turn my car on after a few hours with the climate control setting on floor, the air begins to blow out of the vents at first before it builds up enough vacuum.

Is this normal? I cant remember, takes only about 10-12 seconds to change over. I was thinking maybe I had a leak down occuring, but was not sure if that is how it normally is.

My vacuum lines all appear in good condition and a few have been replaced, newer pcv valve too. Admittingly, my vacuum ball is not in place, its capped off at the end of the line, but I was thinking that only would affect driving on inclines / heavy acceleration. With it missing, my 4x4 even still works just fine. All of my vents change as expected after this and i dont hear any hissing under the dash.

When I switch to AC mode when the car is first turned on, I have rough idle and it bogs down a little under acceleration. I have cleaned my MAF and Throttle body well, but want to try and zero in on a vacuum leak first before spending money someplace else.

Would appreciate any knowledge anyone has.

 

A visual inspection is often not sufficient. The under-hood vacuum lines can become almost brittle and start deteriorating with slow leaks in the beginning. Another failure is when the hose loses its elasticity and then a leak forms where a hose is attached to a ****** vacuum fitting.

I'd do a full check of the hoses to make sure they are not damaged. From what I've seen, these hoses seldom last more than 15 years. Also, I think the vacuum reservoir should help even if the truck has been off for a few days.

The rough idle could also be due to a vacuum leak. The under-dash vacuum lines are of better quality and I have seldom heard of them leaking.

What year Blazer do you have and which type of transfer case do you have? If it one with the Auto-4wd function, the vacuum lines are a bit different.