Car: 2006 Chrysler SRT8
Join Date: Apr 2007
Thanked 1,991 Times in 1,800 Posts
hmm...idle speed variation without any throttle input, right? Mine hunted for an idle RPM for a while after I got the car tuned but now it's settled in to the same idle in D (700 RPM) and rises a bit if idling in Neutral, which is normal.
There could be plenty of reasons for idle variation: vacuum leaks past the throttle, clogged idle air passages, bad or clogged idle air control valve (IACV), dirty throttle body, faulty electronic throttle, problems with the wiring or connectors, ECM problems, etc. Sometimes the carbon deposits in the idle air control valve can cause it to be stuck open or closed. Sometimes even low coolant level can cause the idle fluctuation and the code P0505. Problems with the EGR and EVAP systems also can cause the code P0505. If the idle air control valve or the throttle body is dirty, sometimes cleaning the either one can solve the problem. However, in many vehicles the idle re-learn procedure must be performed after the repair is finished. In some cars, the idle re-learn procedure is performed with a scan tool, in others the ECM re-learns the idle speed after the engine is run for some time.
What I would do is make sure the coolant level is at the proper level and replace the IACV.