more idle troubles

[QUIKSVT]

I'm so burnt out on chasing this damn thing... I have replaced TPS, MAF, IAC. The car starts up, runs up to 1900-2000 rpm, and sits there. If I rev it to say, 3000 it will stay there and fail to drop back down for atleast 10 seconds.

When I shut the car off, it makes a loud noise like a deep tone air horn or something, so I'm guessing it has to have a crazy air leak somewhere, its obviously running lean because it builds heat QUICK.

I plugged in the IAC and watched it with key-on and it appears to stay shut, its hard to blow through. I bought a replacement, which did exactly the opposite and stayed open no matter what. I'm so confused.

 

[HISSIN50]

Did the replacement need to be mounted upside down (there might or might not have been instructions about doing this in the box).

I cant remember your first thread exactly (you had one of many lately and I get foggy on details). Does the car idle normally if the IAC electrical connector is disconnected?

Otherwise start checking vac leaks, as you know. A stockish motor should pull nearly 20" hg at idle - it sounds like you would see a noticable difference if you put a gauge on a line.

Good luck.

 

[QUIKSVT]

I have put a guage and its pulling around 20, but its really hard to tell with the motor idling at 2000 rpm. There is a horrible noise, sounds like a trombone, echoing through the intake. I wish I could explain it. I've checked EVERY vac line, replaced everything from the throttle body forward. Tommorow, I'm pulling the intake manifold, it has to be a blown manifold gasket or something.

 

[QUIKSVT]

Disconnecting the IAC does nothing.

 

[HISSIN50]

Is the vac reading pretty constant/consistant (or does the needle dance)?
If you cover the TB opening with your hand (this will get the idle down), does the resonance change?

Just tossing out random things I would fart around with to change the noise to see if I could locate it.

Good luck and bump.

 

[QUIKSVT]

the resonance just changes with rpm, not completely going away. A couple weeks ago, I noticed this noise I speak of when I would shut the car off. I wondered about it, but didn't let it both me.

The vacuum is pretty consistent with rpm.

The noise doesn't sound like its external, I've listened and listened, and it honestly sounds like its being echoed out from within the motor.

What are the odds of a bad manifold gasket? Do they go bad? Would a FUBAR IAC make such a racket?

P.S. I'm nearly positive the IAC I picked up from the auto part store is no good.

 

[tording]

this may sound kind of odd but you may wanna check your exhaust manifold bolts. I had a manifold bolt back out one time and it make this horrible engine noise like your describing. It sounded like my motor had blown or something and it just ended up being an exhaust leak but did not sound like a typical exhaust leak. something easy to check.

 

[QUIKSVT]

I was right. Returned the new IAC and picked up another, it worked.