Recently developed an intermittent high idle..only when the engine is hot..replaced the iac less than a month ago and it went away for a while. When the problem occurs , it isles at about 1200rpm but will jump to 2k when trying to brake, and 3k when put in park. Replaced some shot vacuum elbows and the tb gasket and it got a little better (no more 3k in park, and only occasionally jumps when braking). Checked for a vac leak 3 separate times..I do get a fair amount of oil entering my intake through the PCV valve not sure if it has anything to do with it but will be replacing that today..any suggestions would be appreciated. Thanks.

 

1. For your high idle, I'd check the power brake booster. Not unusual to develop a pretty good sized vacuum leak there when they fail.

2. The 4.0 has a CCV system, not a PCV system; there is no PCV valve. I think your CCV system may be clogged. I'd recommend removing the valve cover, thoroughly cleaning the inside of it, replace both of the CCV grommets and both hoses (around $45 from either the dealer or aftermarket), replace the valve cover gasket, reinstall valve cover and see where you are it. It is not that uncommon for these to clog on the 4.0. It is necessary for this system to be clean for the engine to breathe properly.

 

thanks for the info

 

With a "tip of the hat" to tjwalker, you may also have a faulty TPS.