high idle
Elder User
Joined: Jun 2006
Posts: 805
Likes: 3
Sounds to me like you possibly have a vacuum leak somewhere. Is the idle a little rough too? Check the throttle body and make sure the adjustment screw hasn't been moved. That's a stop screw, and is only intended to keep the throttle plates from jamming in the venturis. Next, pull all the hoses off the intake except the MAP and fuel pressure regulator. Cap off the nipples, and connect a vacuum gauge to one of them. Start the engine, and check the vacuum and see if it idles slower. Vacuum should be between 18 and 20 inches, idle somewhere around 600. (the number 572 sticks out for some reason). Don't forget the vapor recovery cansiter connection. I don't know where it is on the I6, but it goes right between the two barrels of the throttle body of the 5.0. Since it's on the throttle body, and the least needed piece of equipment, it's a great place to hook up the vacuum gauge while you're looking for the leak.
If the vacuum is low, and the idle high still, check the IAC and make sure it's working. While everything's still disconnected, pull the connector off the IAC, and you should notice a slight change in the idle. Rev the engine quickly and let the throttle snap shut. The engine should nearly stall when you do this. Reconnect the IAC, and do the same with the throttle. It should idle back down smoothly. This is assuming the throttle plates are closing completely.
If the vacuum is good, and the idle comes down when you start the engine, start re-connecting hoses one at a time to find your leak, or at least which hose it's coming through. There's a lotta vacuum driven devices, and any of them could cause idling issues.
If the vacuum is low, and the idle high still, check the IAC and make sure it's working. While everything's still disconnected, pull the connector off the IAC, and you should notice a slight change in the idle. Rev the engine quickly and let the throttle snap shut. The engine should nearly stall when you do this. Reconnect the IAC, and do the same with the throttle. It should idle back down smoothly. This is assuming the throttle plates are closing completely.
If the vacuum is good, and the idle comes down when you start the engine, start re-connecting hoses one at a time to find your leak, or at least which hose it's coming through. There's a lotta vacuum driven devices, and any of them could cause idling issues.
Lead Driver
Joined: Feb 2002
Posts: 7,966
Likes: 595
From: Greater Austin, Texas
If you yank the PCV hose and cap it, you are going to get a reduction in idle speed that may fool you. The PCV is a "known" vacuum leak. You need to check the hose by checking the idle with the hose off and capped versus you putting your finger over the end of the PCV valve. If they are the same, then you leave it alone. It's a vacuum leak you need.
