High idle sounds like a vacuum leak. Most likely the intake lower plenum to the heads ( sealant an gasket breaks down from heat )( just did mine)
Check the vaccum line from intake to brake booster(mine was spongy and would not let vacuum through )most likely behind intake under EGR valve
If your handy the intake should take about 8hrs in your garage. By the way most aftermarket manuals do not list the proper method for the reinstallation of the intake.
Also be careful when disassembling and reassemble the intake - it is very easy to brake off the return hose to the power steering pump (its in the way)
It costs $79 - $99 if you brake it off.
and check that vacuum line while you have the intake off!
If your careful you can do the job for about $40 or less and 8 hrs (+ $11.00 for the vacuum line)
I may get corrected on this but I was quoted 3.5 hrs at the local shop + parts
Good Luck
Mark