1996 Buick Century 3.1L V6 - Throttle Hesitates While Parked (updated)

For some reason the engine hesitates when revving it while in Parked position (listen to attached sound file.) It doesnt seem to do this while moving except it doesnt accellerate quickly unless I “floor” it.

I ran the gas tank down and added new fuel, and then changed the air filter. I know another owner, same everything, but worse. His Century idles real rough and has replaced fuel filter and various vacuum modules to no avail.

Now typically, the dealers mechanic likes to say, “Well charge you for a full diagnostic, then rebuild your fuel injection system,” and still pretend to not know what the problem is while charging me up the wazoo, even if they are aware the symptom is a known problem with certain makes and models such as mine.

So I ask you, dealer et al, is this a KNOWN-problem? Besides the common visual problems like broken/missing vacuum lines, fuel filters, etc., what not-so-easily identifiable problems are common with this vehicles fuel-injection? Modules?

Thanks much.

Your problem MAY be related to a faulty IAC valve and/or dirty throttle body.

Check for intake air leaks too. Like around the air filter housing, loose bolts in the plenum, etc.