strange vaccum problem

[speadfreak]

I am having a problem that hopefully somebody here can help me with. The car has a bone stock speed density motor. The problem is that no matter what I do, I cannot get the idle to come down lower than 1500. The throttle body is closed all the way and is still revving. There are no vaccum leaks(as far as gaskets), but it is obviously sucking air from somewhere. If I pull the PCV valve out while the engine is running and plug the end of it with my finger, the car idles beautifuly(after idle screw is put back to proper position). Also, when the engine is running, if you take the tube off of the valve cover (the one that goes to throttle body), air is being sucked into the engine through this hole.....wait.....there's more.....There is a vaccum line that goes from the vaccum tree on the underside of the intake that ends at the MAP sensor. If I pinch this line off, the engine will spit and sputter or even stall out. I know that on my last two mustangs (which both had mass air)there wasnt even a line going to the MAP sensor. The car runs very good besides the idle, doesn't smoke, only has 48K miles on it. It does lean out if you get on it, probably because its getting more air than the computer realizes, I would imagine.......................please help!!!!

 

[BlownFiveLiter]

Spray carb cleaner around vacuum lines, intake gaskets, etc. If you have a rise in RPM, you'll find a leak. Have you pulled codes at all?

 

[vristang]

If I pull the PCV valve out while the engine is running and plug the end of it with my finger, the car idles beautifuly(after idle screw is put back to proper position). Also, when the engine is running, if you take the tube off of the valve cover (the one that goes to throttle body), air is being sucked into the engine through this hole!!

Can you clarify which way the air is being sucked via the VC/TB hose?

I had very similar issues, and was not able to resolve them. One thing that did help was putting a restrictor in the VC/TB hose. You can find a 1/8" vac line adapter (with male - male fittings) at any parts store. This limits the quantity of air that is being pulled from in front of the TB through the crankcase and into the intake manifold. All of this air is unmetered. The restrictor should work for you.

jason

 

[jrichker]

Spray carb cleaner around vacuum lines, intake gaskets, etc. If you have a rise in RPM, you'll find a leak. Have you pulled codes at all?

I think that this is a good idea, but I would use motor oil or something less likely to flash fire. Burning the hair off your arms & eyebrows isn't cool...

 

[speadfreak]

ok, I found the problem. Somebody had taken the intake off and when they put the gaskets back on, they had them out of place. So the vaccum leak was coming from the lifter valley area. This would explain why spraying carb cleaner had no effect on the idle. It was sucking so much air through the crankase that when I capped off the small hose fitting on the oil filler tube, it started sucking oil and smoking out the exhaust(but the idle did come down when i capped it). ...................I knew I wasn't crazy, I knew it was a vaccum leak

 

[vristang]

ok, I found the problem. Somebody had taken the intake off and when they put the gaskets back on, they had them out of place. So the vaccum leak was coming from the lifter valley area. This would explain why spraying carb cleaner had no effect on the idle. It was sucking so much air through the crankase that when I capped off the small hose fitting on the oil filler tube, it started sucking oil and smoking out the exhaust(but the idle did come down when i capped it). ...................I knew I wasn't crazy, I knew it was a vaccum leak

I had that happen
http://forums.stangnet.com/showthread.php?t=534062&page=4
that should show how far off my gasket was.

jason