02 Neon Flutter idle in park and neutral Codes p1684, p0171, p0422, p0455, p0456
 

Good day,

Need a little help fixing my idle issue on my 02 neon. Car starts fine, but revs to 3000rpm for a second or 2 then idles down to 1500rpm and flutters. It only does this in neutral or park. In Drive or Reverse it idles down to normal, while driving when i let off the gas petal it doesn't idle down so its pretty much like having cruise control on all the time, i even pick up speed without using the gas petal. Braking is fine but the odd time it feels like the car wants to jump forward.

Codes that i have were off the dash using the key on/off while holding the odomerter reset.

i know P1684 is battery disconnect, not worried about that one.

i had codes P0422,P0455,P0456 for quite some time, replaced the gas cap, air filter as recommended for that but my car did not have any gas milage or performance issues and the codes still come up. not too worried unless this is a clue for the P0171.

P0171 seems to be tricky from what i've read, everything from 02 sensons, plugs/wires, injectors, vaccuum leak, fuel pump..

This fluttering idle issue while in park and neutral has to be a clue but i can't really find anything about it. i'm not really wanting to spend a ton of cash, i was planning on selling this thing in the spring and i'd like to keep this as cheap as i can.

P.S. I am not an advanced mechanic. Keep it simple and thanks for any help!

Update: Got code P1294 today, target idle not met. Check engine light came on on my way to work today, went for lunch and it was off, still off now, still has the idle flutter.

Sounds like possibly a vacuum leak after the IAC. First thing I would check is the large flexible hose between the throttle body and intake manifold. That hose can crack and cause some crazy idle problems.