I have a 99 LS teg and I barrowed my buddys OBDII scanner and my check engine code is P505- Idle System Malfunction.

I only get this code when its very cold outside 30 degrees and colder, car will throw the check engine light and then start to rev back and forth from 1250-1500RPM. Lke i said this only happens when its really cold here in KY.

Think the IAC needs to be cleaned and or replaced? Maybe an Air temp sensor?

Thanks for the help in advance!
Craig

 

my 2000 ls did the same thing, clean, or possibly replace your IACV, i cleaned my old one, but ended up buying a OEM valve ($200)

 

In my haynes book.. the p505 error code is <U>IAC valve system fault</U> I would search for a thread on how to clean your IACV, and go from there