My truck idles at around 1100 rpms. There are no vacuum leaks and the motor only has around 1500 miles on it since it was rebuilt so i highly doubt that it is the plenum gasket. There is a strong vacuum in the driver side valve cover and every time I start the truck it revs to around 2300 rpms for a few seconds. It's throwing code p0505 which is for the idle air control system. I'm at my wits end with this truck. This idle is driving me crazy. Any help will be very appreciated.

 

Pull the throttle body, and clean it, pay particular attention to the IAC well, and ports. If that doesn't change anything, replace the IAC.

 

I have already cleaned the throttle body and the iac and everything. The iac looks like it is staying completely closed when the truck is idling. also when i plug up the hose that goes from the valve cover to the air box the truck idles fine

 

Does the IAC open up when you plug that hose? What about if you disconnect the PCV hose on the other side? (and cap the hole.....) May be a bad PCV valve. (stuck open.)

 

The pcv valve has already been replaced and i'm not sure about the iac. i'll have to look here in a second to see if it opens

 

the iac looks like it is staying pretty much closed all the time. even when i plug up that hose

 

Then you have a vacuum leak somewhere.

Plug the hose from that goes to the air box. (disconnect from air box, stuff something in it.)

Pull the PCV valve completely. Plug the hole in the valve cover, and the vacuum port at the intake.

Remove oil fill cap, start motor.

You should feel a breeze coming OUT of the oil fill. If you still have vacuum there, then you have a leak somewhere, and the intake is probably going to have to come back off.

How does your oil look?

 

I plugged everything up and there is still a vacuum coming from the valve cover. If you put your hand over the oil fill hole it will try to pull your hand in. And I found that if the hose coming from the valve cover stays plugged too long I lose all oil pressure. The oil looks good but it does use a little which I was told was because it was still a new motor. This is the craziest problem I have ever heard of.

 

You have a vacuum leak. Unfortunately, it's internal. Intake needs to come off, and be resealed.

 

I suspect plenum. I would take it back where it was rebuilt. Was it doing this when you got it back?