when i first join
i remeber a thread about some kids XJ started to sound like it had a turbo. i seriously doubt that my jeep is making it self turbo charged. back to the point i went wheeling to day, at a creek near my house. some water nothing to deep and some light mud. now it whistles at my around half throttle. im thinking its a vaccum leak, but what do i know.
-Ian
So check for a vacuum leak! The mud/water could be coincidental, or you could have cooled off something hot and caused the leak.
Things to check:
1) Get a can off carburettor cleaner, let your engine idle, and fog the stuff all around the vacuum lines. If it gets sucked in anywhere and the idle ramps up for a moment, you've found a leak. Mark it or fix it and finish the check.
2) You don't mention your year, but I'm going to guess 1987 based on your moniker (get in the habit of telling us from the off - don't make us guess. You get better answers that way...) The MAP sensor gets its signal from the Passenger side of the throttle body - the MAP is on the firewall on a little bracket, just follow that line forward. The rubber bung on the end of the line actually has
two plugs on it - one for the line and one is just a retainer that goes into a blind hole. I've known this to come loose plenty of times - coat the bung that goes into the
blind hole with a little RTV and stick it back in. It just gets loose, and needs a little help.
3) When doing the vacuum leak check, don't neglect the bottom of the throttle body and the manifold-to-head mating surfaces, especially at the back. I find loose manifold screws quite often back there...
4) Also, don't forget that earlier rigs with the NP231 had CAD (Central Axle Disconnect) up front, and this was vacuum actuated. That means vacuum lines. They come up in the passenger rear corner of the engine bay.
5) And the little vacuum tank behind the front bumper (stores nothing to help the HVAC and CAD work.)
6) I usually find it worthwhile to just automatically check the manifold screws once per year - or whenever I suspect a vacuum leak that can't be readily found. A couple have usually worked loose, and it's the work of a few minutes to nip them up again. If they haven't been loose too long, that solves that little nuisance. If they have, your gasket may have burned through and will want replacing - search elsewhere for my tips on how to handle that little job...
Those, anyhow, are my first thoughts. Good luck! Let us know if none of that works...
