Hello,
I have an '03 Neon ES (2.0) with 153000 on it.
I recently changed the head gasket. I also changed the timing belt/tensioner, water pump, drive belts, plugs/wires, and finished with an oil change. This morning I got it all back together and started it up. It started great, but was idling very high, and seemed to be accelerating. I think I am hearing a hiss (vac leak?) but I don't want to let it run too long like it is in order to find the leak. Any thoughts on what might be the problem? I had thought maybe the throttle cable had gotten kinked, but the throttle plate looks closed (car off and air filter out). Everything is connected as it should be.
Thanks for your help.
PB

 

I was going to suggest a vacuum leak, and if you are hearing a hissing noise...
Sounds (no pun intended) like you need to get looking for disconnected vacuum lines.

 

Run car and use brake cleaner. Spray on all Vacuum line connections and lines themselveswhen you hear the engine lower in RPM youve found your leak make sure to check all lines. Then replace leaking part/parts and test.

 

Thanks for the input. I did find a large leak between the Intake Manifold and the Throttle body (bellow tube?) The bottom of the tube wasn't completely on the intake. Runs great now!
PB