Check your PCV, it could be stuck open, also your line from the filler neck to the TB should still be hooked up.

 

PCV is fine.I checked that the other day and the tube to the filler tube is hooked up.As soon as you pull the tube off or take the oil fill top off the idle goes down.

 

I replaced head gasket and had this same problem, idled at about 1200 instead of 750. the intake manifold was pulling air out of the valve galley. watch you oil level, this could indicate the intake is not sealed along the bottom

 

Well your going to be pulling vacuum in the crankcase. When you pull the cap off, your creating a vac leak.

If you pull the tube off from the TB to the filler neck, there should be no change at all, unless the elbows are collapsing or there is something clogging it. That tube is not suppose to have vac to it, it's just a vent.

 

Im gonna spray along the intake and see if there is a leak somewhere this evening.I ll recheck the vent tube to.Like I said though the idle goes right back down when I pull either the oil cap off or vent tube.

 

Crankcase ventilation goes from throttle body (pressure) into valve cover and eventually makes its way up to the intake (vacuum) and gets burned in combustion.

It would seem to me that there could be a blockage at the supply side.

 

Well I sprayed all around the engine checking for vacuum leaks and there was no change in the engine whatsoever so I have eliminated that,especially around the intake.The vent tube isnt stopped up nor is the vacuum port on the throttle boby.I messed with the timing and that didnt do anything for it.I have the TB screw screwed all the way out and it still idles at about 1300 rpms.I tried resetting the computer that didnt work.What else could I try?I didnt have this problem before the head swap

 

my problem was below the intake. hi idle after replacing the head gaskets and INTAKE gaskets.you cannot spray the bottom side of the intake manifold, in the valve galley area. Ie where the lifters are. mine was pulling unmeterd air from the valve lifter galley into the intake manifold. This cause a lean condition and the computet tried to compensate. I had a steady idle at 1200rpm. I was pulling a vacum thru the oil dipstick.

check to see if your using oil, after redoing the intake manifold gaskets my problem went away

 

The tube coming off the throttle body should not be hooked to a vacuum source, only the vent on top of the throttle body.
If you remove the hose and plug the vent tube on the filler neck, and remove the PCV valve and plug the intake, it should not create a vacuum. If it does, your intake gaskets are leaking.

 

Okay.........the tube going from the filler to TB is a .........FRESH AIR INLET......... that is right.

At idle the PCV is sucking blowby and oil vapor from the crankcase, and the fresh air inlet is allowing,,,,hold on, you guessed it, fresh air to enter the crankcase............THAT IS HOW IT WAS DESIGNED.


Therefore you should witness, a slight vac at the filler tube, at 675-725 rpm....~~3"Mg vac.


When the engine idles at 1500 rpm........do you think the vac produced by the engine will be higher or lower than at 700rpm????? You guessed it again.... more vac.


since you are seeing alot of vac at 1500rpm, at the fresh air inlet, YOU can conclude NORMAL.


Your idle is set by the ECM, NOT BY THE THROTTLE STOP SCREW,,, its not a carb.

 

Pull the pcv valve out with the engine idling and see if there is still vacuum in the crank case. If there is, you have intake gaskets leaking into the valley. Seen this on a few cars.

 

Or plug the pcv and spay some sort of fuel into the oil fill tube,(propane or carb clean). If the engine rpm speeds up then you have a internal intake leak.

 

Holy crap, do NOT do this. You do realize that combustion can leak in the crankcase right? You also realize when you put propane or fuel into it you are essentially creating means for combustion in the crank case? Do you really want your engine to explode from beneath and take out a whole bunch of stuff?

And carb cleaner, that can wash the bearings right out. Please don't tell anybody to do this ever again, I don't want to read about a stanger having a dipstick tube lodged in their eye.

 

Well looks like the intake gasket is leaking.So im gonna replace it.I cant remeber the gasket number I had before but it was a MR Gasket kit and I didnt like it but it was free and I put it on anyway.Can someone suggest a good gasket?

 

go with felpro. i had a similar problem, do your valve covers have breathers in them? one valve cover has the filler in it and the other should have a breather. i had a ton of vac on my crankcase and all i did was put a breather in the opposite valve cover and the idle dropped and she ran great.

 

".....the tube off from the TB to the filler neck....it's just a vent."

"the tube going from the filler to TB is a .........FRESH AIR INLET......... that is right."

You're both right - partially. When vacuum is present in the intake manifold (idle, light cruise, decleration) the throttle body/valve cover tube serves to let metered make up air enter the crankcase (FRESH AIR INLET). This PREVENTS a vacuum from being pulled on the crankcase. When vacuum isn't present in the intake (w.o.t) the throttle body/valve cover tube acts as an additional path for crankcase pressure to vent into the throttle body/intake (VENT). THE FLOW IN THE HOSE IS BI-DIRECTIONAL.

If your pcv valve/hose/screen are functioning properly and you're pulling a vacuum on the crankcase the path from the throttle body to the oil filler neck nipple must be blocked somewhere I'd think.

 

the gasket between the intake manifold and the heads is leaking ....underneath...

this is common at the lower edge of from one or three ports.
pull it off and look carefully at any impressions of the gasket... not that you can do anything other than replacing the gasket.

the head surface is usually pretty squatre to the block surface,...but it is common for the intake manifold to get "bent" or twisted...
if it is real bad, then have it remachined in the proper mill / broach.... but I caution that many sho-ps just do not know HOW to do this accurately.....

 

Not only is it a risk for explosion, it will tell you nothing. The PCV system is pulling the crankcase gasses right back into the intake anyway. If you apply propane to the crankcase, there would be no way to discern the difference between an idle increase being from an intake gasket leak in the valve galley or from the propane being pulled into the intake through the PCV system. An intake leak to the valve galley wouldn't affect all cylinders. A better way to diagnose it would be to look at the plugs. Cylinders with a large intake leak would indicate a lean burn on the plugs.

 

If you read his post, it said "plug the PCV"...

 

Im gonna try and replace the intake gasket by next weekend and I will let you know how it came out.Thanks to all for the advise.

 

LOL..

 

You could have a warped intake too. Take a straight edge to it.

 

Jesus christ some times you guys amaze me, it's just an intake gasket leak and Kato hit the nail on the head!

 

The engine will not explode by adding fuel source, propane or anything else. This is common practice in automotive diagnostics for pin pointing a vac leak. go grab any service manual or even hook up a snapon scanner and that info is in there. Just trying to help, and i would never give advice on here that would put any member in danger. thanks.

 

interesting

 

Well got the intake gaskets changed and back together this evening and thats deffinently what was wrong with it.It runs stronger and smoother than before.The idle is great also.